Tea: cultivation to consumption 9789401050272, 9789401123266, 2012022022, 5355365515, 6036276346, 9401123268

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Tea

Tea Cultivation to consumption

Edited by

K. C. Willson

Consultant in Tropical Agriculture, Department of Environmental and Evolutionary Biology, University of Liverpool and

M. N. Clifford

Leader, Food Safety Research Group, School of Biological Sciences, University of Surrey

I~ 111

Sprtnger-Sclence+Buslness Media, B.V.

First edition 1992

© 1992 Springer Science+Business Media Dordrecht OriginaUy published by Chapman & HaU in 1992 Softcover reprint ofthe hardcover lst edition 1992 Typeset in 10/12 point Palatino by J&L Composition Ud, Filey, North Yorkshire TSBN 978-94-01 0-5027-2

o 442 231419 l(USA)

Apart from any fair dealing for the purposes of researeh or private study, or eriticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permis sion in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduetion outside the terms stated here should be sent to the publishers at the UK address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publieation Data Tea: cultivation to consumption I edited by K. C. Willson and M. N. Clifford. - lst ed. p. em. Includes bibliographical referenees and index. ISBN 978-94-010-5027-2 ISBN 978-94-011-2326-6 (eBook) DOI 10.10 07/978-94-011-2326-6 1. Tea. 2. Tea trade. 1. Willson, K. C. (Ken c.) II. Clifford, M. N. (Michael N.) SB271.T27 1991 641.3'372-dc20 91-22774 CIP

Contents

Colour plate section between pages 300 and 301 List of contributors Foreword by H. Ferguson Acknowledgements Preface

XlI

XVll XIX

xx

1 Historical Introduction

J. Weatherstone

1.1 China - 2000 years of tea 1.2 The discovery of the tea plant in north-east India 1.3 A river journey of a thousand miles 1.4 The way forward - the introduction of the plantation system 1.5 The first Indian tea 1.6 Tea in Ceylon: planted in the ashes of the coffee bushes 1.7 Early pioneering by the Dutch 1.8 Conclusion Bibliography

1 6 8 11 14 17 20 22 23

2 Botanical classification of tea

B. Banerjee 2.1 Introduction 2.2 Problems in tea taxonomy 2.3 Features of taxonomic importance 2.4 The tea varieties 2.5 The true tea species 2.6 The 'non-tea' teas 2.7 Key to species and sub-species 2.8 Tea hybrids and the genetic pool 2.9 Hybrid differentiation 2.10 Tea germplasm and wild tea 2.11 Future thrust References

25 25 27 30 33 37 39 39 41 46 47 48

Contents

VI

3 Selection and breeding of tea

B. Banerjee 3.1 Introduction 3.2 The selection process 3.3 Selection criteria for yield 3.4 Selection for quality 3.5 Selection for seed varieties 3.6 Vegetative propagation 3.7 Hybridization 3.8 Clonal seed variety 3.9 Interspecific hybridization 3.10 Inheritance 3.11 Non-conventional breeding 3.12 Breeding strategies 3.13 Conclusion: the future trend References

53 54 55 60 62 66 70 72 73 74 75 77 79 81

4 Climate, weather and the yield of tea M. K. V. Carr and W. Stephens 4.1 Introduction 4.2 Growth processes: a basis for comparison 4.3 Climatic variables 4.4 Commercial yields: case studies in Eastern Africa 4.5 Conclusions Acknowledgements References

87 88 94 115 130 131 132

5 Soils C. O. Othieno 5.1 Introduction 5.2 Formation and types of tea soils 5.3 Classification of tea soils 5.4 Identification through indigenous vegetation 5.5 Chemical properties 5.6 Physical properties 5.7 Biological properties 5.8 Management of tea soils 5.9 Uprooted and replanted tea land References

137 137 140 141 141 155 161 163 168 170

6 Tea crop physiology T. W. Tanton 6.1 Introduction 6.2 Crop development and components of yield

173 174

Contents 6.3 The relationship between photosynthesis and yield 6.4 Dormancy in shoots 6.5 Effect of temperature on shoot growth 6.6 Effect of dry air on shoot growth 6.7 Effect of day length on shoot growth References

Vll

180 183 185 190 194 197

7 Field operations: 1

K. C. Willson 7.1 Choice of site 7.2 Land clearance and preparation 7.3 Erosion control and drains 7.4 Provenance of plants 7.5 Tea seed production 7.6 Propagation 7.7 Field spacing 7.8 Field planting 7.9 Infilling and interplanting 7.10 Shade and shelter 7.11 Weed control 7.12 Irrigation 7.13 Hail References

201 202 202 208 209 209 217 218 219 220 221 222 222 223

8 Field operations: 2

K. C. Willson 8.1 Bringing into bearing and pruning 8.2 Rejuvenation of old plantations 8.3 Harvesting 8.4 Mechanization of field operations 8.5 Fuelwood and diversification 8.6 Other products from tea References 9 Mineral nutrition and fertilizers D. Bonheure and K. C. Willson 9.1 Introduction 9.2 Loss of nutrients 9.3 Outline of nutrition 9.4 Effects of individual nutrients 9.5 Organic fertilizers 9.6 Foliar analysis 9.7 Practical fertilization

227 239 241 249 259 261 263

269 269 270 271 290 296 304

Vl11

Contents

9.8 Symptoms of nutrient deficiency and toxicity 9.9 Use of growth regulating chemicals 9.10 The effect of fertilizers on tea quality References

311 318 319 321

10 Pest and disease control in Africa P. S. Rattan 10.1 Introduction 10.2 Pests and their control 10.3 Diseases and their control 10.4 Pesticides and their application References

331 331 341 350 350

11 Disease control in Asia P. V. Arulpragasam 11.1 Introduction 11.2 Effects of diseases on tea production 11.3 Disease management in tea 11.4 Common diseases of tea References

353 353 355 360 373

12 Pest control in Asia N. Muraleedharan 12.1 Introduction 12.2 Crop loss 12.3 Important pests 12.4 Ecology of pests 12.5 Pest management 12.6 Future strategies References

375 375 376 397 403 408 408

13 Green and semi-fermented teas T. Takeo 13.1 Introduction to green tea production 13.2 A brief history of the production of shade grown green teas-Ten-cha, Gyokuro and Ceremony tea (Matsu-cha) 13.3 The cultivation and production of steamed, unshaded green tea (Sen-cha) 13.4 The production of pan-fried green tea (Chinese green tea, Kamairi-cha) 13.5 The character of green tea 13.6 Semi-fermented tea (oolong tea) References

413 414 417 423 423 443 454

Contents

IX

14 Production of black tea M. G. Hampton 14.1 Introduction 14.2 Raw materials and products 14.3 Principal stages of processing 14.4 Process engineering considerations 14.5 Air utilization in tea manufacture 14.6 The withering stage 14.7 Leaf disruption 14.8 Fermentation 14.9 The drying operation 14.10 Sorting and fibre removal 14.11 Fuel and power 14.12 Packing and transport of tea References and further reading

459 461 463 463 467 478 481 490 494 500 503 509 510

15 Speciality and herbal teas M. J. E. Gill 15.1 Speciality teas 15.2 Herbal teas 15.3 Specific origin of camellia tea 15.4 Specific occasion teas 15.5 China tea 15.6 Flavoured teas 15.7 Teas with historical associations 15.8 Packaging format 15.9 Decaffeinated tea 15.10 Organically grown tea 15.11 The future Appendix 15.1 Grades of black tea Appendix 15.2 Types of tea Appendix 15.3 Herbal teas and their benefits

513 518 519 522 522 523 524 524 525 527 528 529 530 533

16 Instant tea M. Saltmarsh 16.1 Introduction 16.2 The production of instant black tea References Patents

535 536 551 553

x

Contents

17 The chemistry and biochemistry of black tea production-the non-volatiles A. Robertson 17.1 Introduction 555 17.2 Green leaf polyphenols 555 17.3 Polyphenoloxidase 563 17.4 Black tea polyphenols 564 References 597 18 Tea aroma J. M. Robinson and P. O. Owuor 18.1 Introduction 18.2 Biogenetic pathways of the aroma compounds in tea 18.3 Changes in the composition of the aroma complex due to agronomic, cultural and manufacturing practices 18.4 Use of the aroma complex in chemotaxonomy References

603 627 634 638 639

19 The world trade in tea R. van de Meeberg 19.1 Introduction 649 19.2 History 650 19.3 The International Tea Committee and the distribution of 660 world tea supplies 19.4 Prices and auctions 661 19.5 Delivery of tea and payment of accounts 665 19.6 Distribution 666 19.7 Production, consumption and promotion 668 19.8 The future 670 19.9 Alternative packaging for bulk tea 672 19.10 FAG Meeting, May 1989 674 19.11 Instant tea 676 19.12 Comment on 1989 data 676 19.13 Update July 1990 680 19.14 Postscript September 1990 682 19.15 World production and exports of green tea 685 19.16 Provisional data for 1990 685 References 686 20 Impurities, quality standards and legislation R. van de Meeberg 20.1 Impurities 20.2 Standards 20.3 Legislation References

689 692 698 705

Contents

Xl

21 Physiological and clinical effects of tea

V. Marks 21.1 Introduction 21.2 Water 21.3 Tea as a beverage 21.4 Caffeine 21.5 Polyphenols 21.6 Coronary heart disease and serum cholesterol 21.7 Tea and the gut 21.8 Trace elements and vitamins 21. 9 Herbal 'teas' 21.10 Conclusions References Glossary Index

707 707 709 712 729 731 732 733 733 733 734 741 751

List of contributors

P. V. ARULPRAGASAM graduated B.Sc. at the University of Madras, followed by M.Phil. at Wye College, University of London and Ph.D. from the University of Sri Lanka. He was trained in tissue culture at the Beltsville Agricultural Research Center, USA, and is a Fellow of the Institute of Biology, Sri Lanka. He is now Head of the Plant Pathology Division of the Tea Research Institute of Sri Lanka and leads the team which has developed in vitro propagation for tea. B. BANERJEE was awarded M.Sc. at the University of Calcutta, M.S. at the University of Illinois and Ph.D. at the University of London. He was a Nebuta Fellow at the University of Wageningen, IDA-World Bank Visiting Professor at the University of Nairobi, and several times British Council Visiting Fellow in UK Research Organizations. He has visited China at the invitation of the Chinese Academy of Agricultural Sciences and Tea Research Institute. He rose to high rank at the Tocklai Research Station of the Indian Tea Research Association before being appointed Adviser to the TRA. His work and publications have attracted many awards. D. BONHEURE graduated in 1957 as Ingenieur Agronome A.LA.Lv. at the Catholic University of Louvain. He worked initially on tea and quinine at the Institut National pour L'Etude Agronomique au Congo (INEAC). Then he was at the Institut BeIge pour la Recherche Scientifique Outre-Mer (IBERSOM). Returning to INEAC, he became Director of the Station de Recherche Agronomique at Kisozi, Burundi. Since 1966 he has been with the Institut Franc;ais du Cafe et du Cacao (IFCC) (later the Institut de Recherches du Cafe et Cacao (IRCC), which is part of CIRAD (Centre de Cooperation Internationale en Recherche Agronomique pour Ie Developpement)). Originally Head of the Tea Research Station at Sahambavy, Madagascar, he was later seconded to the Cameroon Development Corporation as Chef d'Operation, then Technical Adviser.

Contributors

XUl

Finally, he was at CIRAD Headquarters at Montpellier, France until retirement. M. K. V. CARR graduated in Agricultural Sciences at Nottingham University in 1966. At the Tea Research Institute of East Africa he started the Ngwazi Irrigation Unit. His work at Ngwazi and at Kericho Headquarters earned a Ph.D. from the University of Nottingham. He was then at Wye College, London, before joining Silsoe College. Initially Lecturer in Irrigation Agronomy he became Professor and Head of Department of Agricultural Water Management in 1987. In those posts he has continued with research on, and management training for, Tea; working mainly with the industry in Africa and Bangladesh. M. N. CLIFFORD obtained his B.sc. from the University of Reading in 1968 and his Ph.D. from the University of Strathclyde in 1972 with a thesis devoted to the phenols of coffee. He is currently Senior Lecturer and Leader of the Food Safety Research Group in the School of Biological Sciences at the University of Surrey. His research interests encompass the characterization and analysis of phenols and tannins in foods and beverages; formation and transformation of phenols during food processing; phenols and sensory astringency; the physiological significance of dietary phenols and their metabolites. These studies have produced over 40 scientific publications and, with K. C. Willson, Coffee: Botany, biochemistry and production of beans and beverage, a companion to the present volume. M. J. E. GILL has been associated with the tea trade and the marketing of hot beverages for over thirty years. He has held key positions with Young and Rubicam (Typhoo teas), David Pearce (Brooke Bond), Tea and Coffee Division of Brooke Bond, London Tea & Produce Co., The London Herb & Spice Co., and Premier Brands. The latter incorporates: Ridgways, Melrose, Typhoo and London Herb & Spice Co., thereby holding a major proportion of the speciality and herbal tea market. In 1989 he was awarded the Daily Telegraph Business Sponsorship of the Year Award for sponsoring The London Mozart Players. M. G. HAMPTON graduated B.Sc. in Aberdeen and Ph.D., D.I.C. at Imperial College, London. He was a post-doctorate Fellow with the National Research Council of Canada and is a member of the Royal Society of Chemistry. He started with ICI Ltd (Agricultural Division Scottish Agricultural Industries) involved in research, design, and management of chemical plants. He then worked with Brooke Bond Liebig on design of extraction and drying plants, becoming Head of Engineering. From 1975 he has been Director and proprietor of AFP Consultants Limited. This company provides specialist design and

XIV

Contributors

consultancy services for food processing plants, both in the UK and in developing countries. Work on many crops has included the design, building and operating of a novel instant tea process. V. MARKS graduated in Medicine at Oxford University and is a Fellow of the Royal College of Physicians of London, the Royal College of Physicians of Edinburgh and the Royal College of Pathologists. Since 1970 he has been Professor of Clinical Biochemistry at the University of Surrey and Head of Department of Clinical Biochemistry and Nutrition at St Luke's Hospital. He is best known for his work on the investigation and treatment of diseases of carbohydrate and fat metabolism, but has also engaged in research on alcohol and abuse of drugs including caffeine. He is currently President of the Association of Clinical Biochemists, Medical Consultant to The Tea Council and a VicePresident of the Royal College of Pathologists.

R. van de MEEBERG started his career as a junior tea taster with van Rees in Rotterdam. Fifty years later he retired from van Rees as Managing Director, becoming Managing Director of Vriesthee until 1988. He was knighted, Officer of the Order of Orange Nassau, at the end of 1974. He served as President of the Netherlands Association of Tea Importers and Exporters for many years and Secretary of the European Tea Committee from 1974 to 1988. Advice, based on his long experience in tea, is readily given and is the strength of his appointment as Adviser to the European Tea Committee. N. MURALEEDHARAN earned his Ph.D. in Zoology at the Entomology Research Institute, Loyola College, University of Madras. He has followed his interest in the ecology and control of tea pests with the Zoological Survey of India and, for the last ten years, as Head of Entomology at the UPASI Tea Research Institute. C. O. OTHIENO graduated in Soil Science, B.5c. at the California Polytechnic University and M.Sc. at the University of Manitoba. He was awarded a Ph.D. by the University of Nairobi. After brief periods with the Kenya Ministry of Agriculture and Shell Chemicals he joined the Tea Research Institute of East Africa. He was, in turn, Hydrologist and then Head of Crop Environment Department before becoming Director of the Tea Research Foundation of Kenya in 1981. He has produced numerous publications on plant/water relations and plant nutrition. P. O. OWUOR graduated in Chemistry at the University of Nairobi. At Case Western Reserve University, Ohio, USA he was awarded an M.Sc. and Ph.D. After two years lecturing at the University of Nairobi he was appointed Head of the Chemistry Department at the Tea Research Foundation of Kenya. He conducts research on the relationships

Contributors

xv

between cultural practices, nutrition and manufacturing methods and the quality of tea from which he has authored over 80 scientific papers. In 1987 he was awarded the Third World Academy of Science Award. He has spent short sabbatical leaves at Research Institutes in Japan and UK. P. S. RATTAN graduated in Botany at the University of the Punjab, followed by M.sc. in Botany and M.sc. then Ph.D. in Plant Pathology at the University of Exeter. He has always worked at the Tea Research Foundation of Central Africa, starting as a volunteer with the UK VSO organization. He has continued studying the pests and diseases of tea in Central Africa and is now Senior Plant Pathologist and Entomologist. A. ROBERTSON left the University of Bath with degrees of B.Sc. and Ph.D. He then undertook a post-doctoral Fellowship at the University of Cambridge on black tea polyphenol chemistry, spending 18 months in Malawi working at the Tea Research Foundation of Central Africa. After two years research on large-scale purification of enzymes he joined Campden Research Association. As Head of Chemistry and Biochemistry he expanded the Department whilst retaining special interests in polyphenol chemistry, analytical technology and service quality. He was promoted to Head of Food Science Division in 1988.

J. M. ROBINSON qualified as a Licentiate of the Royal Society of Chemistry. After seven years as an analyst with Lancashire County she joined the former Tropical Products Institute (TPI). Specialization in flavour chemistry led to work on tea quality, particularly aroma, flavour and taints. She is now a self-employed Consultant, having recently left the Overseas Development Natural Resources Institute (successor to TPI). M. SALTMARSH received his B.A. in Chemistry at Oxford in 1968. He has worked in R&D with Mars Inc. since 1972, where he is now Product Development Manager. He led the team which developed a novel process for the production of instant tea which is now in use in Europe. W. STEPHENS graduated in Ecological Science at Edinburgh University followed by an M.Sc. in Soil and Water Engineering at Silsoe College. He worked for a firm of consultants in the UK then as an irrigation agronomist in Malawi before returning to Silsoe College on an ODA tea research project. He has since been appointed Lecturer in Irrigation Agronomy at Silsoe and maintains his interest in tea. T. TAKEO graduated from the Agriculture Department of the University of Tokyo in 1953. He was awarded a Doctorate by the University of Nagoya in 1967. After graduation he was posted to the National Research Institute for Tea; in 1984 he was appointed Director of the Tea

XVI

Contributors

Technology Division. In 1986 he became Senior Chemist at the ITO EN Company, a post he still holds. T. W. TANTON graduated in Botany at Hull in 1967. He received his doctorate in Botany in Southampton in 1970. He is now lecturing in Tropical Farming Systems at the University of Southampton's Institute of Irrigation Studies. Prior to joining the Institute he specialized in crop physiology, spending several years at the Tea Research Station at Mulanje, Malawi, where he studied the productivity of the tea bush.

J.

WEATHERSTONE admits to having few academic qualifications. Coming from a family who have been planters in the East since the 1880s, he too went on to become a tea and rubber planter in Ceylon from 1950 to 1957. His well illustrated book about the early British tea and coffee planters, The Pioneers, was published four years ago. K. C. WILLSON graduated in Chemistry at University College, Swansea, and worked in the chemical industry for several years. He joined the Tea Research Institute of East Africa in 1962 and worked on a wide variety of problems. Reading University awarded him Ph.D. for his work on tea nutrition. This was followed by five years as an Information Scientist in UK, during which time he was elected a Member of the Institute of Information Scientists. His interest in tea continued with consultancy work. In 1974 he became Senior Lecturer in Plantation Crops at the University of Papua New Guinea. Since leaving in 1979 he has carried out consultancy work on various tropical crops, including tea, in several countries for a number of companies and aid agencies. He was in Senegal for two years for the UK Overseas Development Administration. With Dr Clifford he edited the companion volume Coffee: Botany, biochemistry and production of beans and beverage. He is a Chartered Chemist and Fellow of the Royal Society of Chemistry.

Foreword

Tea is a unique crop and, incidentally, a very interesting and attractive one. The tea bush, its cultivation and harvesting do not fit into any typical cropping pattern. Moreover, its processing and marketing are specific to tea. Thus the Tea Industry stands apart and constitutes a self contained entity. This is reflected in the title given to this book, Tea: Cultivation to consumption, and its treatment of the subject. The book is logically planned - starting with the plant itself and finishing with the traditional'cuppa'. Every aspect of tea production is covered, inevitably some in greater detail than others. However, it gives an authentic and comprehensive picture of the tea industry. The text deals in detail with cultural practices and research, where desirable, on a regional basis. The technology of tea cultivation and processing has been developed within the industry, aided by applied research which was largely financed by the tea companies themselves. This contributed to a technically competent industry but tended to bypass the more academic and fundamental investigations which might bring future rewards. The sponsorship of research has now widened and the range and depth of tea research has increased accordingly. The editors and authors of this book have played their part in these recent developments which are well reported in the book. To put together an authoritative, comprehensive volume such as this is a major task and the editors, Dr Willson and Dr Clifford, are to be heartily congratulated on doing so, so successfully. The subject matter of the book involves several disciplines and the editors have made an excellent selection of authors, each an expert in his own subject. They have not only successfully presented their own particular subjects but have integrated them into the picture as a whole. The result is a well coordinated and very readable volume for which each and every author is to be congratulated. Tea: Cultivation to consumption is thus an up-to-date, authoritative

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Foreword

textbook on tea production. Who will read it? Certainly everybody interested in the tea industry will consider it essential reading. It should be on the bookshelf of every tea company, every tea broker, every tea estate and every tea research establishment. Old stagers, whose active days in 'Tea' are over, will read it with interest and pleasure but with regrets that it was not available when their 'Tea' career started. H. Ferguson Formerly Director of the Indian Tea Association Scientific Department, now the Tea Research Association of India

Acknowledgelllents

No multi-author book can be produced without its contributors. We thank them for their efforts, particularly those who joined us at later stages when others had to withdraw. We must not forget those senior persons who have permitted, often encouraged, their staff to contribute, and the Institutions concerned. The services, particularly libraries, of the Universities of Liverpool and Surrey, have played vital roles in the production and editing process. Mr G. A. Penson of Brighton and Mr A. V. Knowles of Liverpool University gave most valuable help by translating or interpreting Russian texts. Our wives have helped in many ways. Marjorie drew the tea shoot used in Chapters 8 and 9 and has done most of the indexing. Both Jane, with her helpers Helen and Mary, and Marjorie have helped greatly with editing, typing and secretarial work. They have borne patiently the periods when the book claimed our attention to their exclusion.

Preface

One of the editors earned notoriety as a youth for drinking vast quantities of tea. It was poetic justice that brought him by a devious route to the Tea Research Institute of East Africa. Here he fell for the fascination of tea as a plant, a crop and an industry; this fascination remains to this day. The other editor developed an interest in the chemistry of the multitude of compounds which together make the flavour and aroma of tea and other beverages. There has long been a need for a book covering tea from all aspects. We hope that this volume, written as it is by authors of long experience and international repute, will fill a useful niche on the bookshelves of people at all stages of the tea industry. We have aimed to make it as comprehensive a work of reference as possible within the space available and that it will be as useful and as well received as the companion volume: Coffee: Botany, biochemistry and production of beans and

beverage. Tea as a crop, a commodity or a beverage has few vices, as Professor Marks explains, and it does a power of good in many ways. From the countries who depend on tea for much of the wherewithal to live, to the drinker of a cup of tea for pleasure or in times of stress, millions of people depend on it. The tea industry has carried on for many decades without the traumas which have affected several other beverages. Tea is a reasonable institution, by and large run by reasonable people, as one of our authors put it. We hope that these reasonable people will find this a reasonable book. Every effort has been made to ensure the accuracy of the contents of this volume. The editors will be pleased to hear of any errors which have escaped their notice.

Chapter 1

Historical introduction J. Weatherstone

1.1 CHINA - 2000 YEARS OF TEA In 50 years from now, in the year 2041, who, apart from those connected with the tea industry, will know anything about the origins of one of the world's most important beverages - tea. In our present day national newspapers we read - in the frequent polls that are conducted upon every conceivable subject - that a significant number of teenagers, on leaving school, do not even know where to look on a map of the world to find his or her own country, Great Britain! So, what about tea? The customer who casually picks up a packet of tea from the supermarket shelf does not stop to consider the strange history of its contents. Tea is just something one drinks every day after which the packet is thrown away without a second thought. But for those of us who are prepared to delve into its secrets, the story of this much-used beverage is so strange, and was so full of danger to its pioneers that one could hardly drink a cup of tea again without a sense of wonder. This chapter will, I hope, give the reader an insight into the fascinating story of the tea plant which, incidentally, comes from the large family of camellias, so well known to us in our parks and gardens, for the beauty of their flowers and shiny dark green leaves. The tea camellia has been known to man for a very long time - Camellia sinensis, the commercially hll.portant Chinese tea plant. This particular camellia has been cultivated by the Chinese people for certainly more than 2000 years, not, as one might imagine, on large plantations, but on countless thousands of small plots of land where the bushes were numbered in dozens rather than acres. The Chinese certainly knew of the tea plant and its value to them long ago, and had discovered that the infusion of its leaves, if carefully processed, produced a very palatable drink. It is likely too, that the people in the Shan States of Burma and Siam had Tea: Cultivation to consumption Edited by K. C. Willson and M. N. Clifford © 1992 Chapman & Hall, London. ISBN 0 412 33850 5

2

Historical introduction

been using the leaves of the tea plant - at first for medicinal purposes, then as a beverage - for as long as the Chinese. At this stage it is as well to mention briefly something about the home of the tea plant. Quite apart from its original home in an indefinite area to the south-east of the Tibetan plateau, including Sze-chuan, Yu-nan, Burma, Siam and of course the Assam variety in north-east India, the tea plant has undoubtedly been spread by the natives over the centuries. Plants have been found growing near to all the caravan routes between China and India. There were also reports by Europeans, in the late 18th century, of tea plants growing wild at Khatmandu. The typical smallleafed China plant occurs in east and south-east China and has, over the centuries, suffered less cross-breeding, and remains comparatively truebred, whilst the tea found growing in the Shan States of Burma and Siam has been the most hybridized. The Assam indigenous plant was later to become subject to much hybridization, particularly in the 19th century, when large importations of seeds of the China jat were introduced into north-east India. The region in which the Assam indigenous plant had been found extended eastwards through the Naga hills and into Burma. Another original home of the tea plant is in Manipur (Cachar and Lushai); in fact the whole region between upper Assam, and Manipur to the south, connecting up with the Chinese provinces of Sze-chuan and Yu-nan, where the best China tea was grown. So, it will be seen that the tea camellia, C. sinensis and its many cousins, is indigenous throughout the forests of south-east Asia where, in its natural state, it grows into a tree between 30 and 40 feet tall. To return to the origins of tea, which are still cloaked in mystery. It is known that the Chinese were drinking tea in the 5th century AD. It was first carried westwards by Turkish traders who, by the end of that century, had reached the Mongolian border to barter goods for Chinese produce. By the end of the 6th century the Chinese began to regard tea in a different light; no longer was it just a medicinal drink, but a refreshing beverage. In the year 780 AD, there is the first authentic account of tea. This famous book, Cha Ching (tea book) written by Lo-Yu, describes the preparation of the leaf and manufacture. The commercial potential of such a trade in tea was not lost upon the Chinese government, and in that same year it introduced a tax on the produce. During the Sung dynasty 960-1127 AD, a regular trade in tea was permitted by the government across its borders into Mongolia. At about the same time the first tea was exported into Tibet. This poor quality brick-tea was transported by yaks, mules and on the backs of porters, from the western border of China and thence into Tibet. The porters averaged five miles a day along 5000 foot high mountain passes, their loads of tea being so heavy - 300 pounds a man - that they put opium

China - 2000 years of tea

3

behind their ears to deaden the pain caused by the straps and weight. China started supplying Russia with small quantities of tea towards the end of the 17th century, and this was first carried overland by government caravans. Ordinary caravans were made up of between 200 and 300 camels, each of which carried four chests of tea. From the Chinese border this legendary trail lay north-westwards across 800 miles of inhospitable Gobi desert, through Ulan Bator in Mongolia and into Russia, skirting Lake Baykal, to the town of Irkutsk. From there onwards the caravan proceeded almost due west at less than the speed of an elephant, over the great plains of Russia. It is no wonder camels have so often been called the 'ships of the desert'. The round journey took in the region of three years. The first tea to reach Europe came by way of the Dutch who, being busy eastern traders, brought the first consignments to Holland in the early part of the 17th century. All the early supplies of tea entering England were brought over from Holland. Coffee houses started to appear in London in the early 1650s, and it was in one of these, Garraways Coffee House, in Exchange Alley in the city, that the first tea was served to the public in 1657. Thomas Garraway was a tobacconist and keeper of one of London's most famous coffee houses, and it was there, and in others like it, that the merchants of the City met to discuss commercial transactions over, not only a cup of tea or coffee, but a glass of punch, or brandy too . One can imagine the interiors of these early coffee houses; dark and gloomy, with a smoke-laden atmosphere in which all sorts of 'aromas' assailed the nostrils - at least we might think they would, but not a bit of it, to the patrons of the day they would have passed quite unnoticed. In those days many would have arrived by horse or carriage, the only alternative to walking, and the smell of the horse stable and sweat mingled freely with those of tobacco and coffee, whilst the smoke from clay pipes mixed with that coming from the many oil lamps and candles that flickered and burned in the semi-gloom. Therefore, is it not surprising that Thomas Garraway should have wished to expound on his shop-bill, to all his long-suffering customers, the virtues of tea? An Exact Defription of the Grovvth Quality and Vertues of the Leaf TEA maketh the body active and lusty helpeth the Headache, giddiness and heavyness thereof removeth the obstructions of the Spleen is very good against the Stone and Gravel, cleaning the kidneys and Uriters, being drank with Virgins Honey instead of sugar It taketh away the difficulty of breathing, opening obstructions

It It It It

4

Historical introduction It vanquisheth heavy dreams, easeth the Brain and strengtheth the

Memory

Only part of the original is quoted, but I think it safe to say that by drinking tea we are, to use a modern idiom - fireproof! Tea was, at the expense of coffee, soon to become the national drink in the British Isles. From 1689 onwards the English East India Company commenced importing tea directly from China in its heavily armed merchantmen. It is said that Queen Anne was very fond of a dish of tea, pronounced 'tay' in those days. By the mid 1750s tea houses and tea gardens were appearing in and around London. These were ideal places at which the public could meet and gossip over a cup of China tea and light refreshments. Every family would have a tea caddy at home. At first, when the cost of tea was prohibitive, they would usually be of silver or possibly tortoiseshell, as only the rich could afford to take tea in their homes. For the poor, a tin or plain wood tea caddy would suffice. In America too, both tea and coffee were drunk, that is, up until the Boston Tea Party in 1773. The British Parliament imposed duties on various imports into the American colonies after the year 1767. Three years later all duties were repealed except those on tea. The colonists showed their disapproval by boarding merchantmen in Boston harbour, and throwing overboard their chests of tea. It would seem that this 'little party' was to lead to the Americans changing their national drink wholly to coffee. The East India Company's ships monopolized the China tea trade until the year 1833. Its ships, known as 'East Indiamen', took six months to make the long and often dangerous voyage from China to the London docks. By the 1860s a much faster type of sailing ship replaced the former strongly built merchantmen - the Tea Clipper. These sleek, finely built ships could each carry over a million pounds of tea from China to the London docks in four months, while some of the faster clippers could do the run in 90 days. The owners and captains of these fast sailing ships competed fiercely with each other for the honour of bringing back to England the first teas of the season, which were always of the best quality. The tea clippers on their outward passages to China, carried manufactured goods from Britain to ports such as Shanghai and Hong Kong. The ships would then be employed in carrying cargoes of rice up and down the east coast of China, after which they would make their way to the tea ports in good time to receive their cargoes of tea. In China, the tea plant is practically dormant during the winter season, and the first plucking is carried out in the spring, towards the end of April. From these first young tender leaves the best tea is made. After the first spring 'flush' had been taken, and the manufactured tea sent down river in junks to the tea ports, three or possibly four further pluckings were made at intervals of about four weeks, the last of these

China - 2000 years of tea

5

producing a much poorer quality of tea. All plucking was then stopped until the following season. By the end of May the first tea clippers had taken on their cargoes of tea, battened down the hatches, and were leaving their ports on a voyage that would take them three-quarters of the way around the world. Many ships were lost without trace in typhoons in the South China Sea. The first ships started to arrive at the London docks in early September, and the quantities of tea arriving daily built up until the London trade was at its busiest in October. With the opening of the Suez Canal in 1869, the sailing ships, which still had to sail around the Cape of Good Hope, were doomed. These were replaced by the new steamers which, by travelling through the canal, could do the passage in as little as 44 days - just half the time taken by the crack tea clippers. Today, one can see in dry dock at Greenwich, London, one of the most famous of all the tea clippers Cutty Sark. It is always surprising to realize that this fine sailing ship was actually sailing on the high seas bringing us our tea just a little over a hundred years ago. People in the western world had been drinking China tea for almost 200 years, but by the mid-1850s her monopoly of the tea trade was slowly coming to an end. Each successive year saw China's exports of tea falling. The discovery of a similar tea plant growing wild in the remote jungles of north-east India was to lead to a pioneering enterprise of great magnitude in the history of world crop cultivation - Empire grown tea. The year 1887 was the turning point when, for the first time, Britain imported more tea from India and Ceylon than she did from China. Table 1.1 shows the rise in imports of Indian and Ceylon tea, and the progressive fall in the consumption of China tea. In China, methods of cultivation on small plots of land had remained unchanged for centuries, consequently the Chinese could not compete with the new 'plantation' way of growing tea that was to be started in British India. However, although China was to lose most of her once Table 1.1 UK imports of tea

Year 1883 1884 1885 1886 1887 1888 1889

UK imports of UK imports of UK imports of China tea (lbs) Indian tea (lbs) Ceylon tea (lbs) 111 780000 110843000 113514000 104226000 90508000 80653000 61 100000

58000000 62217000 65678000 68420000 83 112 000 86210 000 96000000

1 000000 2000000 3217000 6245000 9941000 18553000 28500000

6

Historical introduction

great leaf trade with Britain and the Empire, she still continued to supply Russia, mainly in the form of brick-teas, which she had been exporting to that country since the early 17th century. Poor quality bricktea had been carried by porters over the high mountains into Tibet, Siberia and Mongolia for hundreds of years, and this trade also remained unaffected by the new Indian and Ceylon teas. Tea drinkers worldwide found the new Indian and Ceylon teas much to their liking, with the result that by the year 1900 China's exports of tea had dropped catastrophically. By that same year getting on for one million acres of tropical jungle had been felled in India and Ceylon, and the land planted up with tea. This was the achievement of the British commercial Empire, not forgetting the courage and determination to succeed under terrible conditions of a new breed of man, the pioneer planters. 1.2 THE DISCOVERY OF THE TEA PLANT IN NORTHEAST INDIA In 1823, a Major Robert Bruce, who was then residing in the province of Assam, was told of the existence of tea plants by Singpho chiefs. The exact location was at a place near Sadiya in north-east Assam, adjacent to Burma. Later, while being shown the wild tea trees, he learnt that the natives were in the habit of drinking an infusion of dried leaves from the plants they found growing wild in the forests. The following year Robert Bruce showed the wild tea plants to his brother Charles Alexander Bruce, who was then commanding HM gunboats on the North-East Frontier. Some of these plants were sent down to the Botanical Gardens in Calcutta, where upon close examination they were pronounced to be of the same family, but not the same species, from which the Chinese manufactured tea. This startling discovery went largely unrecognized; at least, no official action was taken at that time. Years before, in 1788, there had been reports from Sir Joseph Banks no less, followed by those from a Colonel Kyd, of tea plants growing wild in the hills of Nepal. Banks proposed to the Honourable East India Company that, with the importation of tea plants from China to Bengal, the culture of tea would be very suitable to the Hindoos, 'their patient industry and pliable fingers would manage well'. During the following years various proposals were put forward as to the feasibility of growing tea in Nepal, but nothing was actually done about the matter. We next hear of a Lieutenant Charlton of the Assam Light Infantry at Sadiya who, being interested in the flora of the district, found in 1832, similar wild tea plants growing in the jungle close to his garrison. He too, like Bruce some nine years earlier, sent seeds and leaf samples of

Discovery of the tea plant in north-east India

7

the camellia to the Botanical Gardens at Calcutta. It was his report that finally set the wheels in motion within the East India Company. Once started things moved quickly. Although the East India Company had a complete monopoly of the tea trade with China, it was, due to earlier reports from botanists and others, fully alive to the possibilities of growing tea in India. When Parliament abolished the Company's monopoly with China in 1833 it was ready to take some positive action with regard to replacing that trade in some way. In January of 1834 Lord William Bentinck proposed to the Council of the East India Company the setting up of a Tea Committee to investigate and make recommendations as to the most suitable areas in which to grow tea. The Tea Committee decided to send their secretary G. J. Gordon to China in order to acquire tea seeds, as well as tea makers and those familiar with the cultivation of the tea plant. Gordon left Calcutta in June 1834 on the sailing ship Water Witch. It is strange, but when one reads that such a person was sent to China to obtain tea seeds and tea makers, the mind does not consider the high adventure involved in making such a journey. The Tea Committee fully realized the difficulty of the assignment it had given Gordon, for it was an extremely hazardous undertaking 150 years ago to penetrate the interior of an unfriendly country with the object of carrying off tea makers and seeds. It says something for Gordon and the botanists of the day that they came back with 'the goods'. It is interesting to know that the pioneer of the tea industry in Java, J. I. L. L. Jacobson, was himself in China in 1833, the year before Gordon arrived on his mission; Jacobson too had left with Chinese tea makers and seeds - not a popular country for Europeans in those days! Gordon, the botanist Robert Fortune and Jacobson all had nerve wracking experiences while collecting seed in China; the last named having the distinction of the Chinese government putting a price on his head. On his last expedition he only just escaped wi th his life. The Tea Committee's next act was to prepare suitable sites at chosen places in India where it was thought the imported China plants would flourish, with the idea that, if successful, these experimental 'tea lands' could later be handed over to private enterprise for future development. To this effect government secured the services of Charles Bruce, and he was appointed 'Superintendent of Tea Culture' in February of 1835. In China the cultivation of tea was centuries old, and it was also a large and flourishing industry; its secrets had been jealously guarded by the Chinese people. For the government it was a bold undertaking to endeavour to enter into competition with that country. That is why Gordon had been instructed to bring back not only tea plants and seeds, but artisans too. One might not think it, but the skills of the leadcanister maker and tea-box maker alone, were of the utmost importance,

8

Historical introduction

for without him or his knowledge, how could the tea be packed into. chests? It was only after Gordon had reached China that the Tea Committee was able to inform government, in December 1834, that proof had been received that the so-called tea plant found near Sadiya, was indigenous, and that it was the true tea camellia of commerce. By that time it was too late to recall Gordon, and anyway a consignment of some 80 000 seeds was on its way to India. These seeds reached Calcutta in January of 1835. Upon arrival the seeds were sent to the Botanical Gardens for germination, under the direction of Dr Nathaniel Wallich. From this original consignment of China seeds, the resultant 42 000 young plants were allocated to three main areas: 20 000 to the hill districts in the Kumaon in north India; 2000 to the hills of south India, and the remaining 20 000 to upper Assam on the North East Frontier. Of the plants that were put out at different places in the hill districts of north India, only those that were established in the provinces of Ghurwal and Sirmoor met with any degree of success. The small tea growing areas of Ranchi, Dehra Dun and what is commonly known as the Kangra valley, never developed on a scale equivalent to that in the hills around Darjeeling, and only a very small acreage of tea exists in those areas today. The last main trial region mentioned was in the hill districts of south India where a consignment of 2000 plants was sent. Nearly all the plants sent to the Nilghiri hills died, but those that were put out at the experimental farm at Kaity, near Ootacamund, fared best. In 1985, with the help of an assistant from the United Planters Association of South India, I made a search around Kaity, but was unsuccessful in finding any of the original China plants. Others that were planted in the Wynaad were also successfully established, but little progress was made for many years. It was not until 1853 that tea was commercially planted in this region, and the industry expanded slowly alongside that of coffee. It was only in the late 1890s that large acreages were opened up to tea. 1.3 A RIVER JOURNEY OF A THOUSAND MILES As north-east India was the first pioneering area, where the government's first experiments in the cultivation of the tea plant were conducted with both China and Assam indigenous plants, we will look in some detail at this then wild and fever-ridden country where, after little more than two decades, a thriving new industry was going in full SWIng.

It is all too easy for us today to pass lightly over the difficulties encountered in those far off days. The tea operation in upper Assam was

A river journey of a thousand miles

9

being conducted at a distance from Calcutta almost twice that of the entire length of the British Isles. On such journeys into the dark interior, the slow country-craft was poled, and tracked from the banks against the current of the river, and this was the only way of travel, apart from the dug-out canoe - and of course HM's gunboats which, should they have been required, would definitely not have been used for the transport of tea plants. It might put the situation more in perspective to know why the Royal Navy had two gunboats operating 1000 miles up the Brahmaputra from their station at Sadiya. These small vessels, shallow in draught, each carried a 12-pounder gun, and could make their way up most of the tributary rivers that came down from the surrounding hills to the Brahmaputra. A regiment of native infantry, commanded by Lieutenant Charlton, was stationed at Sadiya, and the presence of these forces served to keep the peace, to a certain extent, in this wild and unsettled region immediately after the Burmese had been driven out of the provInce. In the late 1830s there were no regular sailings by government steamers, and only the occasional one went part of the way up the Brahmaputra to Gauhati, the journey onwards being made by countryboat. It was only after the year 1856 that the dispatch steamers proceeded as far as Dibrugarth. For the new tea industry struggling to get established in the wilds of upper Assam, these quaint paddlesteamers were to prove a godsend. In fact, right up until the turn of the century, the main traffic artery of Assam was still the great Brahmaputra river - and its paddle-steamers. Here is an incredible tale of adventure, courage and physical hardship undreamed of in our modem day world. Things could have been easier had the journey been not 1000 miles but 50, or perhaps even 500, and had the tea operation not been in a fever-infested jungle area teeming with wild animals. After the Burmese wars, the province of Assam was ceded to Britain in 1826, but the whole region was still in a turbulent state, and was subject to the incursions of fierce hill tribesmen from the Naga and Mishmi hills that border the plains of Assam. It is difficult for us today to understand the awesome task that faced the first pioneers of the tea industry in India a little over 150 years ago. In March of 1835, the Tea Committee recommended to government that a Scientific Deputation be sent to upper Assam to investigate the region in which the wild tea plants grew. Among their many duties, they were to see and identify the Assam indigenous plants growing in their wild state, and give conclusive confirmation that they were the true tea plants of commerce. Those nominated for the deputation were Dr Wallich, Assistant Surgeon and botanist, Dr McClelland, a geologist, and Dr William Griffith, also a botanist.

10

Historical introduction

On the 29th August the deputation left Calcutta, first travelling north by elephants and ponies to Cherrapunjee, after which their route lay north-westwards to Gauhati, where they were to board country-boats for the remainder of the journey up to Sadiya. After four and a half months travel they reached Sadiya in January of 1836. Here they were met by Charles Bruce who, having already explored the wild tea tracts throughout the Muttack country, was to be their guide. It is enough to say here that there was a disagreement between members of the deputation as to the wisdom of growing the China plant in a region where the indigenous one grew so well. Let us now consider the 20 000 ten-month-old China seedlings that were to make the four and a half month voyage 1000 miles up the Brahmaputra river into the dark jungles of the interior. In November of 1835 eight country-boats left Calcutta with their precious cargoes of tea plants. This considerable number of tender young seedlings, many not six inches in height, were packed in wood boxes and large earthenware pots, and were stored under bamboo mat coverings to shade them from the hot sun. The Botanical Gardens provided a number of gardeners to tend and water the plants, while a Sergeant Moore was in charge. As was the custom with Europeans on such river journeys, he proceeded ahead of the main convoy by fast paddle-canoe. After a protracted journey during which 12 000 of the plants died, the remainder reached their destination north of the Dibru river at a place called Kundilmukh in the vicinity of Sadiya. It would seem from an account by the botanist William Griffith, made later on after he had visited the nursery, that the young China seedlings had not been promptly planted out after their arrival. Those that were eventually established fared badly, for according to Griffith: To my great astonishment, not 500 of the plants were alive. The interval between the plants, as well as around each, had apparently never been subjected to the operations of a hoe, or with any other instrument. Easier said than done! Difficulties in procuring labour to clear jungle for the establishment of a nursery and, more importantly, for its continued upkeep, did not help matters. These China plants were shortly after moved to another better spot close by, and planted out next to a plot of young Assam indigenous tea seedlings that Bruce had collected from the abundant tea tracts in the surrounding jungle. Being a practical man, Bruce was not in the least concerned with the botanical merits of either the China plant or the indigenous one; he simply saw that the latter thrived in its own surroundings against the sickly China type. Although everyone's attention was soon switched from the imported

The introduction of the plantation system

11

China plant to the Assam indigenous plant, importations of China seed continued to arrive in the province, even for many years after Gordon's second visit to China, made at the end of 1836 to secure more tea makers. During these years the China plant became widespread, and the fact that, once established, it is a very prolific seed-bearer, must have accounted for the rapid spreading of the plant, which was later to become known as 'the curse of the tea industry in Assam'. Seed was abundant. At the commencement of the Assam Company's operation, it used all the available seed for its own plantings. This was collected from the wild tea trees throughout the company's many rich tea tracts. Later on, large consignments of Manipuri, Assam and China seed were sent to the newly developing tea areas within India; the last two jats going to Ceylon. Towards the end of the 19th century all jats of seed were still being supplied from various sources in India to Java, Sumatra and the hill districts of south India, who were then increasing their tea acreage rapidly. This was followed in the 1920s by a large shipment of seed from Calcutta to Odessa, when Russia embarked upon tea growing in Georgia, where a considerable acreage of tea was opened. India has therefore played an important role in the spreading of the tea industry throughout the world, while still maintaining a clear lead in production. Gordon's visits to China had not been in vain, for they proved invaluable simply because of the considerable number of Chinese tea makers and cultivators who were to find their way up to the wilds of Assam. They were crucial to the new tea industry, for from who else in the world could one learn the secrets of tea manufacture? 1.4 THE WAY FORWARD - THE INTRODUCTION OF THE PLANTATION SYSTEM As Superintendent of Tea Culture, Bruce occupied himself with the establishment of nurseries, while at the same time looking for tracts of wild tea plants. He had a vast area to cover, especially in the Muttack country, where he found most of the rich tea tracts. Over this region of fever-ridden jungle, the only way to get about from one place to another was, over the shorter distances, on foot or on the back of an elephant at three miles an hour, which was far safer considering the place was stiff with tigers. The only other way of getting around to supervise the scores of scattered tea clearings in semi-cultivation, was by native dugout canoe along the numerous tributary rimers that intersected the whole region. These were just some of the difficulties Bruce worked under, including the problem of communicating with the Chinese and Assamese.

12

Historical introduction

When one looks in a clinical way at the history of tea, one tends to forget the background in which the industry outside China was started. For many of those engaged in one way or another during the early years their reward was death, from for example that ever-present minute raider (the malaria-carrying mosquito), cholera, smallpox, blackwater fever and dysentery, not to mention the Naga and Mishmi hill tribesmen with their bows and arrows. One pioneer planter put down his feelings on the subject: The place hummed with anopheles mosquitoes which were lighted to our persons by thousands of willing fireflies. On a busy night in the rains those mosquitoes that could not settle, awaited their turns in the shadow of the patient, thrown on the walls. The Nagas are a wild race who eat dogs and anything else that breathes however long it may have been dead - which first of all kept me in constant terror of a raid. He was obviously one of the lucky ones for at least his abode had walls! Bruce had observed how the natives cut the jungle in which wild tea trees grew, and how, after a very short time, the tea would shoot again strongly from its stock with new vigour. He noticed too, that the leaves of all the tea trees when growing in heavy shade, were dark green, and being not suitable for 'manufacture' were not collected by the natives. The method he first employed was therefore the same as that carried on by the natives for centuries. He and his men travelled from one tea tract to another collecting the young tender leaves from the wild tea trees. The leaf so collected was then manufactured into tea by his two Chinese tea makers at one of the recognized tea tracts. At first many of these tea tracts were no more than a patch of semi-cleared forest 200 x 160 yards in area (as in the case of Chabwa in 1838) where the wild tea trees had been cut down, and that constituted a 'cultivated tea tract'. His greatest need was for skilled tea makers and those familiar with the correct cultivation of the tea plant. This is why Gordon's visit to China was so important, not as things were to turn out for the procurement of seed bu t for tea makers. At first he had only two Chinese black tea makers, but later Bruce stated: these men had twelve native assistants; each Chinaman with six assistants could only superintend one locality and the tea leaves from various other tracts, widely spread, must be brought to those places for manufacture. Until the arrival of machinery, invented mostly by planters, towards the end of the 1860s, the method of manufacture was that which had been carried out in China for centuries. This knowledge was gained by Bruce from his first two tea makers.

The introduction of the plantation system

13

Bruce had almost insurmountable problems at every stage. The leaf that was collected from far distant and scattered tea tracts, would arrive after hours of transportation in an advanced state of ferment. However, as received it was manufactured in the Chinese manner. Whilst employing such local natives as he could get for the collection of leaf from wild tea trees in the jungle, he also employed certain of the hill men for felling and 'opening out' the best tea tracts. The most successful way of converting a rich tea tract under heavy jungle into what might be called, at this stage, a 'tea clearing' was to cut down in its entirety the jungle. This could not be done without great damage to the underlying tea trees and plants, which were crushed and broken by the fall of timber. After three months drying out the clearing was 'fired'. A year later, after the ordeal by fire, the tea - now in an open sun-filled clearing - burst forth with renewed vigour. All those tea trees not crushed and broken to the ground were pruned down, and from the stocks of each, a dozen or so strong shoots would spring up to form a sturdy bush. Next, young tea seedlings - within the tangled clearingwould be thinned out where necessary and replanted to in-fill all the gaps between the existing plants, thus building up a bari of tea, or a 'tea clearing'. The aim was to have tea plants spaced at six feet by six feet. If the tea seedlings were insufficient in number within the clearing, then selfsown seedlings were taken from the surrounding jungle for in-filling. As in-filling was done with two- to three-year-old slender seedlings, four or five of these were planted close together to form a sturdy bush; again building up a bari of tea, if not in neat rows at least in irregular lines of bushes. Seed was also put out in the tea clearings, and was less costly, labour-wise, than uprooting self-sown seedlings and replanting. The upkeep of these small tea clearings was great as all had to be weeded three times a year if they were not to revert back to jungle. The tea bushes were not the only ones to burst forth with new vigour, so too did the shoots from all the jungle tree stumps, as well as the creeping undergrowth that spread almost a foot a day. All this required continual cutting back until it was eventually overgrown by the tea itself. During the early years of jungle clearance, only the richest tracts of indigenous tea were' opened out' to form tea clearings. With time these small scattered baries of tea were extended to join up with each other, by felling the intermediate jungle and in-filling as described. This was the way the first true tea gardens were formed in Assam. After many years, and with the conversion of all the best tea tracts into pukka tea gardens, the momentum of felling continued, but in jungle containing little or no wild tea. Therefore the need arose for each garden to have its own nursery in which the seeds of the indigenous plant were sown. The resultant young seedlings were planted out in the new clearings in the gardens.

14

Historical introduction

To give some idea just how rich the whole region was in wild tea seedlings and seeds, it is best to quote Bruce's own words, written from the jungles of Jaipur in 1839: In drawing out this report, it gives me much pleasure to say, that our information and knowledge respecting Tea and Tea tracts are far more extensive than when I last wrote on this subject; the number of tracts now known amounting to 120, some of them very extensive, both on the hills and in the plains. A sufficiency of seeds and seedlings might be collected from these tracts in the course of a few years to plant off the whole of Assam; and I feel from my different journeys over the country, that but a very small portion of the localities are yet known. Is this not enough to convince those who might have doubts as to whether or not the tea plant was indigenous in Assam? Some writers on the subject consider the tea plant was not indigenous on the plains, but had been transported from further east and planted - as often found in regular patches. Undoubtedly this has happened in various parts where wild tea seedlings had been carried and planted by the natives. Bruce mentions in other parts of his report that wild tea trees and seedlings were found growing thickly together in heavy tree jungle, virgin jungle. This seems to be the proof. 1.5 THE FIRST INDIAN TEA The very first samples of made tea were sent down river in pint bottles to Calcutta in December 1837. The tea was 'manufactured' from the leaves taken from the indigenous plants growing in the tea tracts at Chabwa, Deenjoy and Tingri in the Muttack region of upper Assam. Later, these samples were sent to London. The imported China plants that had been put out in the nurseries at different locations were at that time too small for plucking. The first historical consignment of Indian tea left Calcutta on the sailing ship Calcutta towards the end of May 1838, arriving at the London docks in November of that year. The auction of eight chests of Indian tea - classified in the Chinese manner as those of Souchong and Pekoe - was held at the London Commercial Sale Rooms in Mincing Lane on the 10th January 1839. The sale attracted great interest from all sections of the tea trade, who had hitherto been concerned only with China tea. The teas sold for between 16 and 34 shillings a pound. The government, having ascertained that the cultivation of the tea plant in India was a feasible proposition, then set about handing over all its experimental tea lands to private enterprise. Early in 1840 two-thirds

The first Indian tea

15

of the East India Company's tea lands were handed over to the newly formed Assam Company, rent-free for a ten year period. The Assam Company also took up leases on various other wild tea tracts to the south of the Muttack country. The company then secured the services of Charles Bruce, which was a very sound move as he was the only person who knew anything about tea, and he joined the company in 1840. It is enough to say here that, over the next 15 years, the only tea to come out of Assam was that produced by the Assam Company. During the early 1850s there were many new arrivals to the region; private planters who took up land on their own account, and most notable among the new-comers was the Jorehaut Tea Company in 1859. With the introduction of machinery came a great saving in labour, especially in the rolling of the leaf. Hand-rolling was a slow and tedious process, and one man was only capable of rolling a maund (80 pounds) of withered leaf, whereas just one rolling machine could do the work of about 60 hand-rolling coolies. Likewise, the Chinese method of firing over brick chulas - open fireplaces with charcoal burning at the bottom and wire sieves above - on which the fermented leaf was continually turned until dried into tea, was also very slow; one large dryer of the 1890 period doing the work of 35 men. And how are those original China plants faring these days? Dead long ago one might presume! The answer is they are still growing strongly; the tea plant is a very hardy species, and it has a very long life. When visiting tea estates in the pioneering region of upper Assam in 1985 I saw and photographed some of the original China plants. Those that had been planted by Bruce at Chabwa, as seed, in 1838, had been abandoned in 1935 or thereabouts (photographed c.1935 by W. H. Ukers). These China plants were shown to me by a very old villager, who was the only person my guide, an entymologist from the Tocklai experimental station, could find who knew of their whereabouts. I saw them as 20 foot trees, overgrown by other trees and thick undergrowth. The China plants at Jaipur - also put out originally as seed - by Bruce in 1838, had also been abandoned about 1935, but unlike those at Chabwa estate, had been brought back into plucking, by collar pruning. Today, they form a neat, almost square block of bushes, surrounded on all sides by fields of Assam bushes and are plucked, on average, 25 rounds a year. Regarding this small block of China bushes, now 150 years old, Bruce states in his full report written while he was residing at Jaipur in 1839 that: I collected 24 pounds of China seeds, and sowed some on the little hill of Tipum in my tea garden, and some in the nursery ground at Jaipur, above three thousand of which have come up, are looking beautiful, and doing very well.

16

Historical introduction

The seed that he collected was from the 1609 China plants that had been transferred and brought into the Muttack region in 1837. At that stage Bruce was still experimenting by planting out both the China and indigenous plants; he had, however, seen the merits of the local plant. It was very moving to stand, up to my waist, amidst the large China bushes, where Charles Bruce must have stood almost 150 years before. Although, when Bruce was there, thick jungle would have hemmed in his small patch of tea. Today it is open, the mosquito, so prevalent in tropical jungle, has gone, so too have the wild animals. In travelling south from upper Assam to the district of Manipur, which also borders onto Burma, we come to another region in which the indigenous tea plant was found growing over a wide area, particularly in the Surma valley of Sylhet and Cachar. Here again, the Assam Company was one of the earliest on the scene. The first tea baries were formed in the mid-1850s, and the first tea garden was opened in 1857. Like the pioneering region in upper Assam, the first gardens were developed from tracts of jungle containing the indigenous plants, and were 'worked up' in the same way, either by planting out seed-at-stake, or self-sown seedlings. Unlike the original pioneering area in the vast province of Assam, comprising the middle and upper valleys of the Brahmaputra river on its south bank, another scene of early operations was in the foot-hills of the Himalayas at elevations of between 2500 and 6000 feet. Tea cultivation was first started in the Darjeeling district in the early 1850s, in an area below the town of Darjeeling. Several thousand acres of forest had been felled and many nurseries set up, in which seeds of the China jat were planted. Although unsuccessful in its trials down on the plains of Assam, the China plant was known to be very suitable for growing at colder, higher elevations. After the first garden was opened in 1857, this tea growing district was extended down to the Terai, where the first garden was opened in 1862. The land to the east of the Teesta river, known as the Dooars, was next explored and in this region the first tea garden was opened in 1874. The tea growing area gradually spread eastwards until it ultimately reached the boundary of Assam. Both in the Terai and western Dooars the China and China hybrid jats were planted, and later, as the area under cultivation extended eastwards, Manipuri and Assam varieties were put out. The botanist Robert Fortune was to make many journeys to China in search of plants, including a certain tea camellia. In 1848 he was sent by the East India Company to that country to procure tea seeds and plants for the trial areas that had been started in the hills of north India. The small-leafed frost-resistant China plant was well suited to the Kangra valley, and the surrounding hill districts. Whilst in China, like Gordon 14 years before, he also recruited Chinamen with a knowledge of tea

Tea in Ceylon

17

culture; such men, he explained, were required to teach the poor Hindoos how to cultivate the tea plant. It was quite a feat in those days for any European to travel in China, as all foreigners were restricted to visiting only those areas in the direct vicinity of the ports. Although the Chinese tea makers were of crucial importance in the starting of the tea industry in Assam they were found to be both troublesome and insubordinate and, as their secrets were learned, they were replaced by local labour. The Chinamen who were later recruited by Fortune, and sent up to the trial areas in north India, were also dispensed with as soon as their secrets had been obtained. 1.6 TEA IN CEYLON: PLANTED IN THE ASHES OF THE COFFEE BUSHES We now come to a country that started its plantation industry in 1825, some nine years before the tea industry was commenced in India. The country was Ceylon and the crop was coffee. No-one knew it at the time, but the coffee estates were soon destined to become the tea estates of today. The coffee planters laid low the primeval jungle at a frightening pace; all day long the crash of the forest giants and the steady click' of axes went reverberating around the mountainsides. Fire, smoke - all in the name of coffee. While the planters were more than fully occupied increasing the acreage under coffee, another very important plant was to make its entry into the country - tea. The first tea seeds to arrive in Ceylon, in December 1839, were sent by Dr Wallich of the Calcutta Botanical Gardens, and these were received at the Royal Botanic Gardens at Peradeniya, near Kandy, in 1839. This importation was of Assam seeds which had been collected from the numerous tea tracts in upper Assam. This consignment was followed in early 1840 by 205 plants of the Assam jat; yet more arriving two years later. The seeds were germinated in the Botanical Gardens, and the resultant plants were sent to different places in the hills for experimental planting, the remainder being put out at Peradeniya. These trial plantings were forgotten by the main body of planters for the next 30 years, as the coffee mania gripped all but a few. But tea did grow. By 1869 approximately 176 000 acres of coffee had been planted, and land on which many of its pioneers had died had become well established estates. Coffee had been King for almost 45 years when, in that same year, a leaf disease (coffee rust - Hemileia vastatrix) spread through the coffee estates, reaching every coffee district within five years. I

18

Historical introduction

At first the coffee men were not unduly worried, and the momentum of felling and planting continued without a break for the next decade, during which time a further 100 000 acres were planted up with coffee. The coffee planters had little thought for the future as the reduction in yields caused by the coffee rust was disguised, to a certain extent, by the increase in acreage and the return of very high prices on the London market. The planters hoped the disease would go away but it did not. As the leaf-fall became greater with each successive year, the resistance of the coffee bushes was weakened until they died. During the next 20 years, up to the early 1890s, upwards of 250 000 acres of fine coffee, planted at such great cost in human toil, was uprooted, burnt in the fields, and tea planted in its place. Conan Doyle wrote of the tea industry: Not often is it that men have the heart, when their one great industry is withered, to rear up in a few years another as rich to take its place, and the tea fields of Ceylon are as true a monument to courage as is the lion at Waterloo. The great amount of tea expertise that had been gained in India, firstly from the Chinese tea makers and cultivators, then by the Assam Company and others, was made available to the coffee planters in Ceylon. The pioneering of a new industry had, to some great extent, already been done, but that is not to detract from what the Ceylon planters achieved. Just two years before the coming of the coffee leaf disease, a small block of jungle had been felled and 19 acres of tea had been planted out on Loolecondera estate by coffee planter James Taylor. This first commercial planting of tea in Ceylon was followed by the shipment of two packages containing 23 pounds of tea in 1872. When visiting Loolecondera estate in 1982, I took two photographs: one was of James Taylor's old one-roomed bungalow, built sometime between 1852 and 1856, and now, but for the still almost perfect 10 foot tall chimney, just a pile of collapsed stone overgrown by jungle. The other photograph was of those first tea bushes, planted by Taylor 115 years earlier, which were in that year still being plucked. More evidence of the hardy tea bush. In the early years of the new industry when money was tight and bankruptcies many, old coffee stores were utilized and converted into crude tea factories. Tea seeds were in great demand, for in a comparatively short number of years, a quarter of a million acres of tea was planted out at between 2500 and 3000 plants per acre, which is an awful lot of tea seed! Large importations of both Assam and China seed were used in those first hectic years of change from coffee to tea. Then, as the new industry progressed, each estate established its own plot of tea seed-bearers from which an ample supply of seed could be obtained for

Tea in Ceylon

19

its own nurseries. This, of course, all took time as it takes approximately ten years for seed-bearers to grow up and come into useful bearing. The coffee men were faced with a truly gigantic task, once they had steeled themselves to uproot their dead and dying coffee. Twelve hundred bushes to every acre were burnt, and once again fires were lit, and flame and blue smoke could be seen on every mountainside throughout the hill districts, this time in the name of tea. During these sad times hundreds of coffee estates lay abandoned, and with no money coming in to pay the labour force, thousands of Tamils returned to their villages in south India, while hundreds of proprietary planters returned to Britain ruined men. Of those that stayed, many underplanted their dying coffee with young tea seedlings, whilst continuing to harvest their dwindling coffee berries, which were still fetching very high prices. Others uprooted all in one fell swoop, and planted tea in the ashes of the coffee bushes. In many cases their labour force went on working without pay, standing firmly by their employers in these hard times. As stability gradually came to the new industry, the first tea factories were built. Some of these shacks hardly resembled a factory, being constructed in a similar way to the 'tea making houses' that were used in India in earlier years. The early factories in Ceylon were made with mud and wattle walls under a cadjan root which was an improvement on those that had been used in the pioneering years in India, all of which had thatched roofs. There was not the added problem of the tea sheds, come factories, burning down as they frequently did in Assam through the heat from open charcoal burning ovens. In Ceylon, the green leaf brought in from the fields was probably withered in separate withering sheds or even on the verandah floor of the planter's bungalow, had it been situated close enough. The withered leaf was then hand-rolled on long grooved tables and fired after fermentation. On the hard-packed mud factory floor there would have been a line of charcoal burning ovens, over which the thinly spread leaf was slowly fired, or dried on shallow bottom trays into tea. Hand sorting of the made tea into different grades was done with Chinese-type bamboo sieves. The Chinese method of hand manufacture was used in India, Java and Ceylon until the coming of machinery. With the arrival of the very solid tea machinery, pukka factories were built with timber on finely dressed stone pillars and a cement floor. These factories of the 1880s and early 1890s were mostly built with just one withering loft, but with the rapid increase in green leaf, most were being built with two or even three lofts by the turn of the century. By the year 1900 there were 380 000 acres under tea, and from then on there was a steady increase until the late 1960s, when there were

20

Historical introduction

approximately 600 000 acres in cultivation. During the past 20 years however, the total acreage has dropped to 522 000. 1.7 EARLY PIONEERING BY THE DUTCH The commercial cultivation of tea in The Netherlands East Indies was started on the island of Java, and in the beginning followed on much the same lines as that in India. About 100 years before, in 1728, the Dutch East India Company had considered planting tea in Java, but, as with the English East India Company in 1788, nothing was actually done. Whereas C. A. Bruce was the pioneer of the Indian tea industry, J. I. L. L. Jacobson was the pioneer of the industry in the Dutch East Indies; in fact he was the first European tea planter. The Dutch East Indies comprised many islands of which the four largest were Borneo (Dutch) (i.e. the greater part of Borneo), Sumatra, Celebes and Java. When Jacobson arrived in Java from Holland in 1827, he already had considerable knowledge of the buying and selling of tea, as he had been an expert tea taster and tea merchant. He was therefore the ideal person for the Dutch government to send to China to collect information about tea culture and manufacture. The first 500 tea plants to reach Java were procured from Japan by the government, and from these Jacobson was able to produce the first black tea in 1829. In that same year he returned with the first plants from China. Like Gordon and Fortune, who were sent to China on the same mission, Jacobson had difficulty in his travels in the interior, for in those days few, if any, Europeans got farther than the seaports. His expeditions were spread over a period of six years, and by the time of his last trip, made in 1833, he had brought back to Java millions of seeds as well as many tea artisans. After its early start the tea industry did not leap forward as it had done in north-east India, and it more or less marked time during the following forty years. Progress, or the lack of it, was very similar to that of the industry in south India which, like Java, did not start to increase its acreage greatly until the late 1890s. With large importations of seed from India and Ceylon into Java, and with the steady elimination of its old fields of China tea, the industry has since developed into being the third largest tea producer in the world - always excepting China, whose production is probably slightly less than that of India. With the experience gained in Java, the industry spread to Sumatra in the early part of the 20th century, and the acreage under tea has since increased to that shown in Table 1.2. The three 'm ain tea producing countries have been mentioned in some detail because it is interesting to know how things started.

21

Early pioneering by the Dutch

There is a comparatively small but well organized tea industry in Japan today. As a close oriental neighbour of China, its tea history goes back many centuries. The first tea was brought from China in the year 801 AD, and planted at Yeisan. Tea cultivation has therefore been carried on for many centuries and, like China, it too was a peasant occupation in which, during the early years, every villager owned a few bushes. Japan consists of four main islands, and it is on the southernmost of these that tea is grown. Because the winters are severe, the small-leafed frost-resistant China plant is cultivated, and a limited number of pluckings are made from late April until early September, with a long wintering period. The tea growing districts roughly correspond to that of Sze-chuan in China. The first European merchants to trade with Japan were the Dutch. Ships of the Dutch East India Company first arrived in Japan in the early part of the 17th century, and at first all manner of goods were traded between the two countries, including tea. It was not, however, until the year 1859 that tea was exported on a commercial scale. From that year until the early part of the 20th century exports grew, but with heavy increases in labour costs during the 1914-18 war, the industry has since not progressed significantly. The Japanese, like the British and indeed the Chinese, are great tea drinkers and consume much of their own tea. It will be seen from Table 1.2, supplied by the Tea Council, that the continent of Africa is now coming into contention with the older producing countries. Table 1.2 Tea production 1989 figures

Country India Sri Lanka Java and Sumatra Japan Kenya

Malawi

Acres 1016000 522000 268000 147000 210 000 46000

Source: Data provided by the Tea Council, London.

Apart from the first three countries mentioned in Table 1.2, which were directly concerned with the actual pioneering of the plantation industry in the east, practically all the other tea growing countries of today greatly benefited by having been able to draw upon the hard won experience gained by the early planters. These tea producing countries

22

Historical introduction

include Africa, French Indo-China, Malaya, Formoso, Mauritius, Iran, Turkey, Russia, the Argentine and Brazil, of all places. The most northerly region in which tea is grown today is Georgia, in south Russia, on the eastern shore of the Black Sea, the southernmost being South Africa, and the Argentine in South America. 1.8 CONCLUSION It was the prying eyes of westerners, who, by their guile, took from China the seeds and plants of its most famous camellia. In the case of the Dutch this was of crucial importance in the commencement of the tea industry in Java, while the British, being endowed with the Assam indigenous plant, could at first manage well without the Chinese tea camellia. In China the traditional peasant way of cultivation and handmanufacture had remained the same for centuries. With the start of the 'plantation' system of tea growing on British owned estates and, in later years with the introduction of machinery, China found it hard to compete. Labour-wise, the great tea industry has given employment to countless millions over the years, not only on the actual estates, but also in the many subsidiary occupations. This has been of enormous benefit to the countries concerned. In Ceylon, for example, there were nearly 500 000 Tamils working on the tea estates by the year 1900. Although there will always be those who say that estate labour has been exploited, it is a fact that, but for the tea industry, thousands of Tamil families would have spent scores of years living in great hardship back in their villages in south India. In most cases they exchanged poverty and part-time work for full employment and better working wages than they could possibly have earned in their own villages. It may seem surprising, but India alone with just over a million acres under tea, probably employs in the region of 1 500 000 estate workers, and if the many subsidiary occupations connected with the tea industry are taken into account, the total could be nearer 2 000 000. Up to Independence in India (1947) four generations of British planters had been involved in the pioneering and running of the industry. The first generation lived in primitive mud and wattle huts while carving out new estates from jungle. After Independence many tea gardens changed hands, and today most are Indian owned. However, there are still some famous old tea companies such as the Assam Company, the premier tea company, George Williamson & Co. Ltd and others, who own gardens. After the nationalization of British owned estates in Ceylon (now Sri Lanka) in 1975, these are now managed by Ceylonese.

Bibliography

23

Over 150 years ago, on the 10th January 1839, the first Indian teas were auctioned at the London Commercial Sale Rooms in Mincing Lane; it would be interesting to know what part tea plays on the world's stage in another 150 years' time. BIBLIOGRAPHY Antrobus, H. A. (1957) A History of the Assam Company, T. & A. Constable Ltd, Edinburgh. Baildon, S. (1882) The Tea Industry in India. Bramah, E. (1972) Tea and Coffee, Hutchinson & Co., London. Bruce, C. A. (1838) An Account of the manufacture of Black Tea as now Practised at Suddeya in Upper Assam, by the Chinamen sent thither for that Purpose. Calcutta. Bruce, C. A. (1839) Report on the Manufacture of Tea, and on the extent and Produce of Tea Plantations in Assam. Calcutta. Forrest, D. M. (1967) A Hundred Years of Ceylon Tea, Chatto & Windus, London. Harler, C. E. (1933) Culture and Marketing of Tea, 1st edn, Oxford University Press, London. Ukers, W. H. (1935) All About Tea, Tea & Coffee Trade Journal, New York. Weatherstone, J. N. (1986) The Pioneers, 1825-1900. The Early British Tea and Coffee Planters and their Way of Life, Quiller Press, London.

CHAPTER 2

Botanical classification of tea B. Banerjee

2.1 INTRODUCTION The genus Camellia includes some 82 species which are mostly indigenous to highlands of south-east India (Sealy, 1958). Tea is the most important of all Camellia spp. both commercially and taxonomically. Since all Camellia spp. do not produce the brew that goes into the cup that cheers (Banerjee, 1988a), taxonomy plays a major role in the identification of true teas among the Camellia spp. for commercial exploitation. Many non-tea species of Camellia are however used as ornamental plants. Tea taxonomy is still a challenge today, but did not receive the attention it deserved possibly because of the complexities involved; interest generally ceased once the taxa of economic importance were identified. Consequently, taxonomy continues to be an area of low priority in the research programmes of most tea research institutes. But information on taxonomic characteristics, genetic diversity and biogeography of Camellia in the living collections and herbaria may still help in identifying genotypes with high productive potentials which could be used as progenitors to improve the existing genetic base of commercially grown tea. 2.2 PROBLEMS IN TEA TAXONOMY Tea is a heterogeneous plant with many overlapping morphological, biochemical and physiological attributes (Purseglove, 1968; Wickremasinghe, 1979; Banerjee, 1988b). Cultivated tea is maintained as a low bush in a continuous phase of vegetative growth: it is therefore essential that vegetative characteristics are correctly chosen to differentiate taxa. But most vegetative characteristics of tea show a continuous variation and a Tea: Cultivation to consumption Edited by K. C. Willson and M. N. Clifford © 1992 Chapman & Hall, London . ISBN 0412338505

26

Botanical classification

high degree of plasticity, and hence, cannot be separated into discrete groups to identify various taxa (Wickramaratne, 1981). Indeed tea has hardly any vegetative feature that can be said to have a discontinuous variation. These drawbacks notwithstanding, leaf pose and leaf macromorphological features, including leaf colour, have been widely used as diagnostic criteria in tea taxonomy. Thus tea was grouped into lightleaved or dark-leaved types on the basis of leaf colour, or high or low jats based on serrations on leaf margin (Eden, 1976). It is difficult to rank or sort out these and related morphological variables in order of their importance, especially in their relative importance, in tea taxonomy: hence an element of subjectivity has always crept in all attempts to classify tea. Taxonomical problems were further compounded by the presence of many local varieties like Manipur, Burma, Lushai, or variants like viridis, bohea, tran-ninh (Watt, 1898; Cohen-Stuart, 1916; Pasquier, 1924), and innumerable intergrades with many overlapping morphological features (Purseglove, 1968). In most cases information on the morphological features, growth habit and distribution of these varieties is lacking. 2.2.1 Tea taxonomy: the Thea-Camellia controversy It is difficult to say if the original description of tea as Thea sinensis by Linnaeus (1752) relates to the species mostly cultivated today. The description was based on a drawing by Kaempfer (1712) of tea (?) collected from Indonesia (Barua, 1965). Later, Linnaeus recognized two species of tea, Thea bohea and T. viridis, and withdrew T. sinensis. T. bohea and T. viridis were separated solely on the basis of number of petals; the former had six and the latter nine. Much later, because of an awarness of the economic importance of tea, extensive collection of indigenous tea was made in forests contiguous to Upper Assam-Burma border. Out of this collection two distinct taxa of economic significance were identified. These were the small-leaved China plant described as the Thea sinensis, and the large-leaved Assam plants, the T. assamica (Masters, 1844). Sealy (1937) made a thorough revision of the genus Camellia and placed most cultivated tea varieties under this genus. But many authors continued to place cultivated tea under the genus Thea. For example, in a taxonomic arrangement used by Roberts et al. (1958), Camellia was considered to be a 'section' under genus Thea: section Camellia in this arrangement included all non-teas, while all known taxa of cultivated tea were placed under section Thea of genus Thea (Table 2.1). This possibly was the reason behind using the term as Thea camellias to describe the tea cultivars (Barua and Wight, 1958; Sharma and Venkataramani, 1974).

27

Features of taxonomic importance Table 2.1

Section under Thea

Section Theopsis Cohen Stuart Camelliopsis (Pierre) Thea (L.) Dyer

Camellia (L.) Dyer

ParacamelIia Sealy (ined)

Taxon Camellia cuspidata (Kochs) Wright Camellia salicifolia Champ. ex Benth Camellia caudata Wall Camellia sinensis (L.) O. Kuntze Camellia sinensis var. assamica (Masters) Kitamura Camellia taliensis (W. W. Smith) Melchoir Camellia irrawadiensis P. K. Barua Camellia hongkongensis Seem. Camellia japonica L. Camellia reticulata LindI. Camellia saluenensis Stapf. ex Bean Camellia pitardii var. yunnanica Cohen-Stuart Camellia sasanqua Thunb. Camellia kissi Wall

Source: Roberts et al. (1958).

For a long time Thea and Camellia were considered to be separate genera, and chemotaxonomical characteristics, particularly the presence of eugenol glycoside in the essential oil of Camellia, but not in Thea was used as a major criterion to separate the two genera (Fujita et al., 1973). But in their morphological, anatomical and biochemical features Camellia and Thea are so much alike that they do not really provide realistic basis for differentiation. Indeed the apparent difference in leaf pose, patina and pigmentation is a part of a total variation in leaf features (Roberts et al., 1958; Sealy, 1958; Barua, 1965). Hence Wight (1962) considered Thea to be synonymous with Camellia and the name Camellia prevailed. But earlier taxonomic confusion also led to a dual nomenclature of tea, i.e. Camellia thea Dyer in India (Wight and Barua, 1939), and Camellia theifera in Indonesia (Cohen-Stuart, 1916). Tea today is botanically referred to as Camellia sinensis (L.) O. Kuntze, irrespective of species-specific differences. 2.3 FEATURES OF TAXONOMIC IMPORTANCE 2.3.1 Vegetative structure

The characteristic leaf and floral morphology, and growth habit are the more important criteria used by Sealy (1958) in assigning taxonomic categories within Camellia. Though because of their plasticity, vegetative characteristics are less reliable in tea taxonomy than the reproductive structures, yet vegetative features have often been found useful in preliminary differentiation of taxa (Wight, 1959).

28

Botanical classification

Vegetative characteristics generally used in assigning taxonomic categories include: 1. 2. 3. 4. 5. 6. 7.

The ratio of leaf length to leaf width. Angle between leaf tip and axis. Petiole length. Leaf size. Ratio of apical lengths. Internodal length. Length and girth of the bud.

These and related characteristics however overlap and show a continuous variation (Table 2.2). Therefore their usefulness in taxonomy is somewhat restricted (Wickramaratne, 1981). Table 2.2 Variability in vegetative characteristics of tea

Characteristics Mean leaf angle (degrees) Laminar angle (degrees) Internodal length (mm) Individual leaf area (mm2) Leaf area index (LAI) Leaf lengthlbreadth ratio Height (cm) Girth at collar (cm) Branching habit Thickness of branches at 60 cm from ground level (cm) Length of internode between the second and third leaves from the apical bud of flush shoot (cm) Length of the third leaf (cm) from the apical bud of growing shoot Breadth of the third leaf (cm) from the apical bud of flush shoot Angle between the third leaf of flush shoot and the internode above (degrees) Colour of mature leaf Pubescence on the bud and abaxial side of the first leaf Anthocyanin pigmentation in young leaves and petioles Dry weight of flush (three leaf and a bud) shoot (mg)

Range of variability 50-120 110-125 15-70 120-200 3.5-8.5 2.0-2.8 184-539 25-42 Acutely orthotropic to plagiotropic 1.4--4.4 0.9-3.2 2.0-6.0 1.5-3.8

35-65 Light green to dark green Glabrous to densely pubescent

Sources: Satyanarayana and Sharma (1986); Banerjee (1987a).

Nil to dark 60-350

29

Features of taxonomic importance

F

........

E

B--'"

A--.

B

Figure 2.1 Longitudinal section of a tea flower. A - Pedicel; B - scars on the pedicel; C - tours or receptacle; D - sepal; E - petal; F - stamen; G - ovary; H - column; I - style arms (after Barna, 1963).

2.3.2 Reproductive structure Unlike vegetative parts, the reproductive characteristics are more discrete and show relatively less variation. They therefore provide more reliable diagnostic criteria. Tea flowers (Fig. 2.1) are formed in the axils of scale leaves, either singly or in clusters. They are borne in the axil following the shedding of the bud scales at an early stage. These flowers are pedicillate, and in the very rudimentary stage of their growth, two or more bracteoles, or outgrowths on the pedicel, enclose the stalk of the flowers. These bracteoles are arranged alternately or nearly so on the pedicel, but may also be located on opposite sides. As the flowers grow, bracteoles are thrown off, though at times they may also persist (Barua, 1970).

30

Botanical classification

The fully developed flower has a persistent calyx usually with five sepals. The petals are white, waxy, usually five, but two additional petals are not uncommon. At their base petals are fused and they are obovate, emarginate and internally concave. Stamens are fairly numerous, vary betwen 100 and 300 per flower. The ovary is composed of three carpels. Wight (1962) recognizes two types of stigma, i.e. the linear stigma and the apical stigma. The style consists of three parts which are united for varying length into a column: the style is of taxonomic significance and could be ascending, geniculate or terminal. 2.4 THE TEA VARIETIES The earliest attempts to classify tea in India (Watt, 1898), Indonesia (Cohen-Stuart, 1916) and Vietnam (Pasquier, 1924) mostly involved recognition of local 'species' or variants on the basis of differences in leaf colour and shape (Table 2.3). Later a comprehensive study by Watt (1908) proved that these local variants or so-called 'species' are essentially intergrades resulting from unrestricted intercrossings between disparate parents. Intergrades therefore form a part of the total variation in the genetic pool of tea, and according to Sealy (1958) cannot be assigned to the status of separate species in their own right. Table 2.3 Variants of tea and their distribution

Variants

Geographical distribution

bohea } Assam-Burma (Irrawaddy basin) stricta viridis Cambodiensis Indonesia Vietnam tran-ninh Sources: Watt (1898); Cohen-Stuart (1916); Pasquier (1924).

Despite marked variation, leaf feature continue to be the basis for classification proposed by Kitamura (1950) and Sealy (1958). Thus, based on leaf pose and growth habitat, Kitamura (1950) and Sealy (1958) recognized two intra-specific forms of C. sinensis (L.), i.e. the China variety, Camellia sinensis var. sinensis (L.) and the Assam variety, Camellia sinensis var. assamica (Masters) Kitamura. The characteristic features that separate these two varieties are shown in Table 2.4. In this classification most of the variants (Table 2.3) were assigned to either of these varieties on the basis of their leaf features, but two 'fixed

C. sinensis var. sinensis f. macrophylla Sieb (Kitamura)

C. sinensis var. sinensis f. parviflora (Miq) Sealy

Sub-varieties

Sources: Kitamura (1950); Sealy (1958).

Assam Camellia sinensis var. assamica (Masters) Kitamura

China Camellia sinensis var. sinensis (L.)

Variety

Leaf features

Tall, quick growing tree

Erectophile

Leaf pose

Large, Planophile horizontal, broad, mostly non-serrated, light green

Small, erect Dwarf, slow growing, shrub narrow, like serrate, dark green

Growth habitat

>700

1, but performance of these types will be below optimum in poorer environments. But, plants with b < 1 from good environments rejected otherwise for poor performance in good environments may turn out to be better performers and will be most suited for relatively poorer environments. Thus a flexibility will make the se1ction process more broad-based, particularly in overcoming the environmental effects on yield. 3.3.6 Competitive ability The competitive status of plants is not generally considered in tea selection, possibly because of over-emphasis on vigour and growth. Besides, competition does not appear too overt in tea because pruning, plucking and a minimal planting distance do not apparently induce competition (Rahman et al., 1981). But according to Cannell et al. (1977) competition can be discerned during the formation of the canopy, and some genotypes with high relative growth rates can outcompete others in productivity. Though competition is also a continuous process in the roots, it is not expressed phenotypically. Cannell et al. (1977) therefore considered relative growth rate of the above ground parts a good approximation to the competitive ability of a plant. This in effect means that plants which are superior in terms of growth than their immediate neighbours have a higher attribute for competition, and this is also reflected in their high yield potential. However, whether relative growth rate by itself is a measure of high competitive ability is debatable because the growth of the above-ground part is also dependent on the state of dormancy (Barua and Wight, 1959) and other environmental factors (Carr, 1972). But if we assume that productive plants are those that yield most per unit of environmental resources like light, water and mineral nutrients available to them

Selection criteria for yield

59

(Donald, 1968), then genotypes capable of utilizing these inputs at their optima must also have high competitive ability. Even with this perspective, it is difficult to say if larger plants considered to have higher competitiveness (Cannell et al., 1977) will optimize these inputs better than others. An added problem is how to identify plants that are 'genetically' large, assuming yield and plant-size are inter-related. A related aspect is that, because of the extreme heterogeneity of tea soils, selection tends to be biased towards those plants growing in good sites (which therefore have good growth), but, as pointed out by Wickramaratne (1981), progenies of these plants may not necessarily turn out to be highly productive unless the specific soil conditions from which the mother bushes were selected are available. Though plants from good soil sites, with better growth, may appear to have higher competitive ability, this may be related more to their distribution in the more fertile section of the soil. Likewise, selection for size, assuming it reflects non-genetic competitive ability, will be biased more towards plants with small neighbours, i.e. on the basis of their spatial position rather than genetic make-up. Nevertheless, in selecting for higher competitive ability, the following aspects are worth bearing in mind. 1. The correlation of yields of individual bushes with the surface area of the plucking table. 2. Whether larger plants tend to have smaller neighbours and vice versa. 3. A comparison of the yield of leaves per unit bush area, and yield per bush with the sum or mean values of competing neighbours. To obtain the former the surface area of each bush must be determined. 3.3.7 Resistance to pests, diseases and environmental stress Very little progress has been made in breeding for resistance to insect, mite or nematode pests, or fungal diseases of tea. However, tea varieties are known to vary in their tolerance or susceptibilities to various phytophagous groups and fungi, and in general this has been related to leaf pose (Banerjee, 1987). Similarly, breeding specifically for drought resistance has not been attempted, but it is recognized that difference in rooting depth is an important factor in drought resistance (Nagarajah and Ratnasurya, 1981). In a cooler climate such as in Japan, where tea remains dormant during the winter, flushing in early spring is considered to be a useful selection criterion as the early flushers are also quick growers (Toyao, 1965). Early flushing is also an important attribute of quality because components of quality, particularly volatile flavour index, in early flushing tea are generally of a higher order (Hazarika et al., 1984). Therefore, early flushing will have an additional advantage from a

60

Selection and breeding

quality point of view as well. But where frost hardiness is required, a late flushing characteristic would be ideal (Harada et al., 1956), though such plants may not be highly productive, or of high quality value. 3.3.8 Summary of morphoselection for yield

The principal characteristics used are summarized in Table 3.2. It is realistic to consider bush area along with plucking points and recovery rate after pruning, i.e. the weight of tippings (the first round of plucking to build up the plucking table) along with branch thickness. The advantage would be the rejection of large-well-framed bushes with open plucking tables, and first-recovering bushes with thin branches - both conditions, if intrinsic, could cause serious yield restrictions. Table 3.2 Characteristics used in the selection of mother bushes for yield in tea breeding

Attributes

Characteristics measured

1. Shoot properties Degree of dormancy Flushing behaviour 2. Leaf size Small leaf (low yielder) Large leaf (high yielder) 3. Growth Weight of prunings Weight of tippings (recovery rate after pruning) 4. Bush area Plucking point density 5. Leaf area Foliage density

In general, the plant characters of interest in selection are: 1. Surface area of the plucking table of the bushes (A). 2. Yield of leaves per unit area of bush (YIA). 3. Yield per bush (y), where Y = (A x YIA).

These three aspects fairly cover plucking point density, bush vigour and growth all of which are of consequence in overall productivity of the bushes, measured as yield per bush. This approach does not however consider anything of the field heterogeneity and inter-plant competition which also affect the selection process (Cannell et al., 1977).

3.4 SELECTION FOR QUALITY Quality is an essential component of tea breeding, but selection solely for quality has not been successful. Wight and Barua (1954) sought to relate morphology with quality from the fact that pubescent types

Selection for quality

61

produce better teas than glabrous ones irrespective of leaf colour. A gradient in quality distribution with pubescence has also been reported (Venkataramani and Padmanabhan, 1964; Wu, 1964). Visser (1969) however believes that a combination of slight pigmentation (by anthocyanin) with pubescence influences quality in Sri Lankan teas. Apart from hairiness, different shades of leaf greenness are also considered to be expressions of quality. Thus quality, expressed by liquor colour, strength and overall aroma, is at its highest in light-leaved varieties but not in dark-leaved ones: hence perhaps the contention that an optimum 'greenness' is essential for highest quality (Wight et al., 1963). Dark-green and pale-green leaves are usually associated with poor quality, but whether the leaf colour is the only factor to influence quality is debatable. Indeed the mechanism of biosynthesis of the complex volatile compounds associated with quality is not always related to any morphological feature (Wickremasinghe, 1978; Takeo, 1984). These drawbacks notwithstanding, pubescence is considered to be a reliable criterion for quality. The degree of pubescence on the under surface of the leaf is however more important for quality purposes. Wight and Barua (1954) have ranked pubescence with quality in the following order of importance: 1. Glabrous leaves with only hair on the mid-rib.

2. 3. 4. 5.

Leaves with a few scattered hairs on the lamina near mid-rib. Pubescence extends about half-way to the margin. Leaves with entire under surface of lamina pubescent. Leaves where pubescence forms a dense indumentum.

A strong correlation (Fig. 3.1) between the ordered arrangement of pubescence and quality suggests pubescence is indeed a factor in tea quality and hence of significance in selection for quality, particularly in orthodox tea. Glabrous plants with good quality attributes are rare. They are more difficult to select, and are of less certain breeding behaviour than pubescent plants. The frequency of calcium oxalate crystals in parenchymatous cells of the leaf petiole - the phloem index of Wight (1958) - is also a useful parameter for assessing quality. Plants with low phloem index are usually of lower quality value than those with higher phloem index (Fig. 3.2). But a strong interaction between phloem index and pubescence suggests an interplay between the two is possibly more important in quality. Phloem index is subject to large variation due to sampling and environmental factors, and more importantly, its phenotypic expression does not permit visual selection for quality in a way the leaf features do for yield. Consequently its importance as a selection criterion is somewhat restricted (Visser, 1969).

62

Selection and breeding

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Figure 3.1 Correlation between pubescence and quality (after Wight and Gilchrist, 1959).

Chloroform test (Sanderson, 1963) and theaflavin analysis (Hilton and Ellis, 1972) have been reported to be useful in selecting for quality in some cases, but not when yield and quality are considered together. 3.5 SELECTION FOR SEED VARIETIES Earliest attempts for mass-selection for seed varieties did not involve any specific selection criteria (Wellensick, 1934a,b), though morphological features like bush size, leaf size, density of plucking points and growth rate were considered in selecting parents that were artificially pollinated to produce progenies (Wight, 1956). The approach was subjective and results were not always commendable, though it helped in producing some of the early jats or varieties of tea. Indeed these older varieties or jats were the primary sources for planting materials the world over in the early part of this century (Singh, 1979). But this approach in massselection, which was restricted to the utilization of the same population, did not improve overall yield, possibly due to a lack of adequate genetic variability. Thus, while elite mother bushes selected from the natural

63

Selection for seed varieties

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30-35°C) on rates of shoot growth and photosynthesis (Hadfield, 1968) are the sometimes concurrent influences of large saturation deficits (SO) of the au.

100

Climate, weather and the yield of tea

Tea production has traditionally been identified with humid, misty areas of the world, but the adverse effects of dry air on growth and production were not quantified until relatively recently. A critical midday value for the SO of about 2.0 kPa above which 'yields' are reduced was originally inferred from other measurements (Carr, 1972). Subsequently, the sensitivity of shoot extension rates to the saturation deficit of the air over the range 1.0 to 3.0 kPa was demonstrated in Malawi by Squire (1979). Ory air surrounding the crop leads to high potential transpiration rates, which can result in minimum shoot water potentials as low as -0.6 to -1.4 MPa in the middle of the day, even when the soil water content is close to field capacity. Shoot water potentials link directly to rates of shoot extension through effects on cell turgor. Squire (1979) also observed that the linear response of shoot growth rates to mean air temperature was obscured completely when the air was 'very dry'. Afterwards Tanton (1982b) showed that the apparent critical SO value which when exceeded caused a reduction in relative shoot growth rates was 2.3 kPa (at air temperatures of 25°C or 30°C this corresponds to relative humidities of 28% or 45% respectively). This has important practical implications since one reason why irrigation does not substitute entirely for rainfall is because it cannot reproduce the humid atmospheric conditions usually associated with rainy seasons. This statement applies to nearly all crops, but particularly to those which are especially sensitive to dry air conditions, such as tea. The contrasting responses of tea to irrigation at Mulanje, Malawi and Mufindi, Tanzania, for example, has been explained by the fact that the afternoon saturation deficit of the air in Mulanje often exceeds the critical value of 2.0-2.3 kPa during September and October, when it is dry, but very rarely in Mufindi (Fig 4.3; Carr et al., 1987). This is an observation of critical importance for it highlights the care that must be taken when transferring the results of irrigation experiments from one site to another, or indeed from one year to the next, if factors such as this are not taken into account. The only way to overcome the effect of dry air on growth is through mist irrigation. That is the application of small quantities of water as a mist at intermittent intervals throughout the middle of the day in order to maintain a humid environment close to the crop. (Note that normal sprinkler irrigation applying water at intervals of 7 to 30 days will not achieve this effect.) Such an experiment was originally done with success by Lebedev (1961) in Georgia (USSR), but more recently a large trial has been initiated in Malawi to see if the encouraging results obtained in a small plot experiment by Tanton (1982b) could be reproduced profitably on a field scale. Initial results appear to be promising (Clowes and Starch, 1988).

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Figure 4.3 Comparison of (a) weekly yield distribution and (b) mean afternoon saturation deficit for Mulanje, Malawi (---) and Mufindi, Tanzania (--). (Redrawn from Carr et al., 1987.)

4.3.3 Soil temperature The possible role that soil temperature may play in controlling rates of shoot growth and yields of tea was highlighted by Carr (1970). He observed in southern Tanzania that when soil temperatures (measured at a depth of 0.3 m beneath a short grass surface) fell below 19-20°C, rates of shoot growth (for clone 1) began to decline, remaining very low at temperatures of 17-18°C. As the soil warmed there was a lag in response, before active shoot extension (although not necessarily bud development) again increased linearly with soil temperature over the range 19.5 to 21.5°C. In Malawi, Fordham (1970) also showed how shoot growth was positively correlated with soil temperature (at 0.3 m beneath a grass surface) up to 25°C, but at soil temperatures above this, rates of shoot growth declined (perhaps linked to large saturation deficits of the air). Tanton (1982b) though was unable to maintain high rates of shoot growth when he used electrical heating wires buried 0.15 m deep in the soil to raise soil temperatures under mature mulched and irrigated tea from 18° to 25°C (at 0.2 m) during the 'winter' months in Malawi.

102

Climate, weather and the yield of tea

This contrasts with the results of Carr (unpublished), Othieno and Ahn (1980) and Othieno (1982) who used different mulches to modify the soil temperatures beneath young tea in Kericho, (altitude 2178 m), Kenya. They found that increasing the soil temperature, with polythene mulches, or reducing it, with stone chip pings or organic mulches, had direct effects on such variables as stem diameter, yield (higher soil temperatures resulted in more axillary buds developing into shoots) and total dry matter production in the two years after planting. The range of soil temperatures covered was 14 to 21°C, measured at 75 mm depth. When the crop cover exceeded 60% soil temperature differences between treatments disappeared. Although organic (grass) mulches serve many positive functions in young tea (for example reducing runoff and soil erosion, conserving moisture and improving nutrient availability), there can be adverse effects in areas where low soil temperatures are limiting. Grass mulches reflect more (0.20) incoming radiation than bare (moist) soil (0.11), leading to reductions in soil temperatures of about 2°C (Othieno, 1982). This can be important, delaying the rate of development of young tea in high altitude areas. Because of shading of the soil by the canopy in particular (Stigter et aI., 1984), and by any surface mulch, soil temperatures under mature tea will be substantially less, about 4°C in Tanzania (Carr, unpublished), than those recorded at a similar depth under short grass at an agrometeorological station. This is an inevitable result of the way in which tea is normally grown. The temperature of 18°C recorded by Tanton (1982b) under mature tea would correspond to about 22°C under short grass, which is perhaps above the upper limit at which soil temperature becomes a limiting factor to growth, whilst 25°C would correspond to 29°C, which may be too hot. Soil temperatures less than 20°C under short grass, or 16°C under mature tea (both recorded at 0.3 m depth) may control shoot extension rates, to the extent (for clone 1) of 8-10 mm week- 1 °C- 1 (Carr, 1970). The mechanisms involved are not clear but may involve hormonal control of partitioning away from the shoots to the roots. 4.3.4 Solar radiation

Incident fluxes of solar radiation (sunshine), particularly at high altitudes near the equator, can exceed 1000 W m- 2 , with local peak values sometimes substantially greater than this due to additional radiation reflected by clouds. Of this total about 20% is reflected by the surface of the crop back into the atmosphere, and a similar total is reemitted as long wave radiation. This means that the net available energy at the surface of a tea canopy can reach 600 W m- 2 (Squire and Callander, 1981). The vast majority of this short-wave radiation is

Climatic variables

103

intercepted by leaves in the top 0.3 m of the canopy, almost regardless of foliage geometry below 0.1 m (Hadfield, 1974b), with only about 5% reaching the ground. Healthy tea, with a flat canopy completely shading the ground, is very efficient at intercepting light. Photosynthesis of single leaves of tea in the field is light saturated at about 350 W m- 2 (Sakai, 1975; Squire, 1977). Whole canopies become saturated at 700-800 W m- 2, a value equivalent to full sunlight in the 'winter' seasons of many high latitude tea areas, and to about 75% of full sunlight in the 'summer' or rainy season (Squire and Callander, 1981). Only a very small proportion of the net available energy is used in the process of photosynthesis; the vast majority is dissipated as latent heat (through the process of evaporation) and as sensible heat (heating the surrounding air). For example, measurements made in Kenya by Callander and Woodhead (1981) showed that almost 50% of the total incoming solar radiation was transformed into latent heat, and 10-15% into sensible heat at the crop canopy. During the dry season the fluxes of latent and sensible heat were similar, each amounting to about 30% of irradiance. These concepts are particularly important when considering the effects of sunshine on leaf temperatures, on the leaf-to-air temperature differences and on the corresponding saturation deficit between the leaf and the air. Thus Squire and Callander (1981) using the above data calculated that in the rainy season the (surface) leaf temperatures would be 0.3°C warmer than the air for each 100 W m- 2 of solar radiation (Le. up to a maximum of 3°C), but in the dry season twice this (i.e. up to 6°C), or even four times (i.e. up to 12°C) if the stomata were completely closed. Leaf-to-air temperature differences of this magnitude have a correspondingly large effect on the leaf-to-air saturation deficits, and hence on shoot extension rates, especially when day-time maximum air temperatures are close to the upper limit for tea (30-35°C). As Squire and Callander (1981) showed, a 10°C leaf-to-air temperature difference when air temperatures are 35°C, increases the leaf-to-air saturation deficit from 1.5 to 5.5 kPa during the monsoon season in Assam, and from 3.0 to 7.0 kPa during the hot, dry season in Malawi. With experimental evidence that shoot extension rates are restricted when the SD of the air alone exceeds 2.3 kPa, declining by 75% at an SD of 4.0 kPa (Tanton, 1982b), and some (conflicting) evidence that stomatal conductances may be reduced by a large SD, the critical importance of evaporative cooling of the leaves (by transpiration) to maintain fast shoot growth rates is clear. (a) Shade This is a complicated and not yet fully understood topic studied in some detail by Hadfield (1968, 1974a,b) in Assam. Shade trees are still

104

Climate, weather and the yield of tea

widely used in tea in Assam and Bangladesh, but only rarely now in Africa. Dense shade can reduce the level of incident radiation to only 200 W m- 2 , but the exact level will depend on the position of individual tea bushes relative to the shade trees, and the type and density of trees used (Hadfield, 1974a). In Assam and Bangladesh maximum daily air temperatures in the summer can often exceed 30°C. These high temperatures combined with high levels of irradiance during the middle of the day may lead to leafto-air saturation deficits in excess of 2.3 kPa, with resultant reductions in the rates of shoot extension and (probably) net photosynthesis (Hadfield, 1968). In such situations shading can prevent leaf temperatures (and saturation deficits) reaching excessively high levels. This normally more than compensates for any loss of dry matter production following a reduction in incident light levels at the crop surface, since a lack of assimilates is not thought usually to limit yield (Squire and Callander, 1981). Cultivars do though differ in their responses, Assamtype bushes with large, horizontally held leaves, being more susceptible to overheating than China-type bushes with small, inclined leaves. The Assam-type cultivar is also potentially lower yielding as a result, it is thought, of self-shading of leaves lower in the canopy (Hadfield, 1968, 1974b). When excessively high leaf temperatures and/or leaf-to-air saturation deficits occur for a substantial period of the year, some protection through shade, particularly for Assam-type cultivars, may be of net benefit over the year. In areas though where the maximum daily air temperature rarely exceeds 30°C, shade is unnecessary and will usually lead to a reduction in the yield of tea. For low-input, low-output systems of tea production, there may be other benefits from this traditional form of agro-forestry. (b) Day length Within the range of day length represented in tea growing areas, for example from a few minutes close to the equator to about 3 h 20 min in Assam (26° 47' N) it appears that day length alone is not responsible for seasonal variation in yield. As Tanton explains in Chapter 6, differences in air temperature, expressed as thermal time, are sufficient to explain the depressions in yield which occur during winter months at high (> 7-8°) latitudes. 4.3.5 Water availability

The water requirements of the tea crop formed the subject of a symposium (Carr and Carr, 1971), and have subsequently been

105

Climatic variables

comprehensively reviewed by Squire and Callander (1981) in an excellent overview. The principal conclusions of that review are summarized here, and updated where new information is available. A sensible approach is to consider each component of the hydrological water balance in turn. Precipitation = Evaporation soil water storage

+ Run-off + Drainage

± Changes in

(a) Precipitation Tea is grown in areas where the annual rainfall may be less than 700 mm as at Chipinga (Zimbabwe), but where irrigation is essential to ensure economic yields, or up to more than 5000 mm in parts of Sri Lanka. The distribution of rain over the year depends on latitude, and is modified by altitude and topographic factors associated with proximity to escarpments, mountains or inland water. In areas close to the equator, there are usually two rainy seasons, which sometimes merge, and two dry seasons of different severity. At higher latitudes the seasons merge into one dry and one wet season. There are also seasonal differences in temperature, with cool-dry and warm-dry periods. In some tea areas snow falls (e.g. Georgia, USSR), protecting the canopy from frost, whilst in others (e.g. in Kericho, Kenya), hail is a serious hazard causing average annual yield losses of about 10%, but reaching 30% in some years (Othieno et al., 1991). (b) Evaporation Whether or not rainfall in any area is adequate to ensure high yields, or continuous production when temperatures allow, depends largely on the prevailing potential evaporation rate. In many tea areas evaporation from a full cover of tea (Ecrop) ranges between 3 and 6 mm day-l (equivalent to 90-180 mm month-I) depending on season. The crop factor is the ratio of Ecrop to Eo, where Eo is the evaporation from an open water surface, usually calculated for tea using the McCulloch (1965) version of the Penman equation. The value of the crop factor for mature tea is normally taken to be about 0.85, which is similar to that for wellwatered crops with complete ground cover. This value has been obtained using a range of experimental techniques, including a largescale catchment water study (Blackie, 1979), a weighing lysimeter (Dagg, 1970), micro-meteorological energy-balance method (Callander and Woodhead, 1979) all in Kenya, with changes in soil water content measured with gypsum resistance blocks by Laycock and Wood (1963) and gravimetrically by Willatt (1973) in Malawi, and with a neutron probe by Cooper (1979) in Kenya.

106

Climate, weather and the yield of tea

Some of the water lost by evaporation from a tea canopy is intercepted rainfall, which Squire and Callander (1981) estimated to represent about 1 mm for each rainfall event. Assuming that there were 200 rain-days a year, this would be equivalent to 200 mm or 0.12-D.14Eo. This suggests that the crop factor for tea which is only irrigated at infrequent intervals, or in the absence of regular rainfall, may be as low as 0.71-D.73. (c) Run-off Until the ground cover has reached at least 60%, there is always a risk that run-off will occur in young tea if no precautions are taken, such as mulches, intercropping or tied ridges (Othieno, 1975, Chapters 5 (pp. 166-9) and 7 (pp. 202-7) in this volume; Othieno and Laycock, 1977). With full ground cover, Blackie (1972) found that surface run-off from an estate in Kenya only represented 1% of the annual rainfall, a value similar to that of the forest it replaced. (d) Drainage When the soil profile is at field capacity, excess rainfall will either run off, or percolate through the soil from the surface before appearing as outcrops of the water table in streams and rivers. How much of the total rainfall this represents will depend very much on local conditions. But as an example, Blackie (1979) found on a mature estate in Kenya that drainage represented 40% of the 2021 mm mean annual precipitation. In parts of Assam, Bangladesh and Rwanda high water tables are a feature of the low lying areas where some tea is grown, and open ditches and sometimes field drains may be needed to dispose of excess soil water. (e) Storage Water is held in the soil, against gravity, by capillary forces acting within the soil pores, and by adsorption onto soil particles, particularly clays. The maximum amount of water which can be retained in this way, corresponding to the water content of a soil when free drainage has ceased about two days after applying excess water, is known as field capacity. This is the upper limit of available water; the lower limit of available water is known as permanent wilting point. The water retained in the soil between these two limits is known as available water, and represents the volume of water which is available for extraction by roots. A certain proportion of this water is considered to be easily available, depending on the soil type, rooting density and potential evaporation rates. At some point as the soil dries below field capacity shoot extension growth begins to be restricted (assuming low temperatures or

Climatic variables

107

large SO are not already limiting) and afterwards, if the soil continues to dry, the stomata begin to close. Irrigation experiments are designed to specify when these processes occur and at what stage irrigation may be economically worthwhile. The amount of available water is represented by the volumetric water content, and ranges from as little as 0.08 in sandy soils to as much as 0.22 in clay soils. In a 5 m deep root zone this would represent 400 or 1100 mm of available water respectively. By contrast in Bangladesh roots may only extend to maximum depth of 1.0 m (in low flats) or 2.4 m (high flats) or 3.6 m (in the tillahs or small hills), but in all cases the total available water content for each soil series is only about 125-175 mm (van der Laan, 1971). With any analysis of this sort, special care must be taken to define: (a) the method of determining field capacity (field or laboratory techniques, and if in the laboratory whether the equivalent suction was taken to be 0.005, 0.01 or 0.033 MPa) and (b) the 'effective' rooting depth. Unfortunately there are as yet no easy rules which have general application. There is much evidence though to show that roots of tea can extend to considerable depths (> 5 m) when constraints such as high water tables, compacted layers, murram, or rock do not restrict root growth. By the end of extended dry seasons, tea roots can extract water from depth. For example, Fig. 4.4 shows changes in soil water content with depth in unirrigated tea over the six months dry weather at the Ngwazi Tea Research Unit in Mufindi, Tanzania (Stephens and Carr, 1991b). At this time the measured soil water deficit was about 300 mm. Cooper (1979) has reported similar results in Kenya. In most tea areas there is sufficient excess rainfall during the rainy season to bring the soil profile back to field capacity prior to the start of the next dry season. Where there is not, irrigation is usually already practised. (f) Summary Squire and Callander (1981) summarized an idealized annual water balance for mature tea, based largely on data from Africa. For total precipitation of 1700 mm, transpiration accounted for 1050 mm (ET = 0.75Eo, Eo = 1400 mm) and interception for 200 mm (200 rain-days, canopy storage 1 mm); stream flow totalled 450 mm of which 430 mm resulted from deep drainage, and 20 mm (1 % of precipitation) from run-off. In this example the annual change in soil water content was only + 30 mm. Since annual totals of Eo in many tea areas are in the range 1300 to 1600 mm, rainfall should average at least 85% of this, or 1150 to 1400 mm if irrigation is not to be essential. These values are similar to the

108

Climate, weather and the yield of tea

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Climatic variables

109

minimum rainfall totals suggested before (Carr, 1972). How this rain is distributed during the year is though clearly important. 4.3.6 Drought mitigation and irrigation Water deficits in plants develop as a consequence of water loss from the leaves as the stomata open to allow the uptake of carbon dioxide from the atmosphere for photosynthesis. In tea stomata are found only on the lower, or abaxial, surface of the leaves at densities of 150 mm- 2 (Squire, 1978) or 166-283 mm- 2 (Renard et al., 1979). The water lost by transpiration from the leaf mesophyll cells is replaced by water drawn from the soil through roots, stems and leaves along the xylem vessels. This is a gaseous exchange process (water vapour for carbon dioxide gas) and the term transpiration efficiency is used to describe dry matter production per unit of transpiration. Alternatively, water-use efficiency describes dry matter production per unit of water lost by evaporation (from the soil or crop surface) and by transpiration. For commercial purposes though it is often easier to compare the water-use efficiency of a crop on the basis of the commercial yield per unit of evapotranspiration (evaporation plus transpiration) or per unit of rainfall and/or irrigation (Turner, 1986). As an example, for a tea crop yielding 3000 kg ha- I y-I of made tea in an area where the annual evapotranspiration is 1250 mm, of which transpiration makes up 1050 mm, the water-use efficiency is 2.4 kg ha- I mm- I, and the transpiration efficiency is 2.9 kg ha- I mm-I. If the total annual rainfall at the same place is 1700 mm, the water-use efficiency (for rain) is 1.8 kg ha- I mm-I. Water-use efficiency values like these, providing they are carefully defined, are a good way of evaluating the effectiveness of various agronomic or drought mitigation practices, and of assessing, in crop yield and financial terms, the worthwhileness of irrigation. (a) Drought mitigation Clones are known to differ in their susceptibility to drought, but little work has been done to quantify or to explain these differences. Subjective assessments are made based on visual appearances in the field during periods of dry weather, and some attempts have been made to explain these differences in terms of physiological responses to drought such as the relative change in the sensitivity of stomata to changes in shoot water potentials. Indeed differences between clones do appear to exist using this index (Carr, 1971a,1977a,b; Renard et ai., 1979) but more work needs to be done to relate such variables to yield. It is important to specify what aspect of drought resistance is important

110

Climate, weather and the yield of tea

(Turner, 1986). For example is it the capacity to survive periods of dry weather with minimum damage (i.e. to endure low tissue water potentials), or to continue to produce crops at this time (by maintaining high tissue water potential)? This is a complicated topic, especially since clonal mother bushes do not always appear to behave in the same way as vegetatively produced siblings (Carr, 1977b), and is beyond the scope of this chapter. It is though of great importance to tea producers in areas with regular dry seasons who are unable to irrigate. The way in which young tea plants are brought into production can influence their sensitivity to drought, the balance between canopy development and root growth being critical (Carr, 1976). This can be described as a problem of 'adolescence' prior to the crop establishing a sufficiently large root system to support a full crop canopy. Drought at this time can also render young tea plants susceptible to Phomopsis theae infection. Irrigation will ensure that young tea comes into production quickly but apart from the work of Willatt (1970, 1971), Fordham (1971) and Othieno (1978a,b) little has been reported on how best to irrigate young tea during the period of establishment, and how to quantify any financial benefits. If irrigation is not an option, other drought mitigation practices for young tea include mulching with or without micro-catchments (or tiedridges) to conserve and/or to store any rainfall (Shaxson, 1971; Templer, 1971; Othieno, 1975). In mature tea, the time of pruning can playa major role in minimizing drought stress. In areas with long, regular dry seasons, particularly when it is initially cool, it is normal practice to prune at the end of the rains, or beginning of the dry weather. The removal of most of the foliage immediately stops transpiration, and the prunings (as long as they remain in the field) act as a mulch. Refoliation of the bushes then occurs using water stored in the soil. In areas close to the equator, where the dry season is also warm, a compromise has to be reached, since the largest flushes occur at the start of the dry season (following the rise in temperature). Pruning then begins after this flush has been harvested, but hopefully before drought stress has caused major damage to the bushes, which will delay recovery from the prune. There can also be problems of labour peaks at this time which may complicate the issue further (Othieno, 1983). As discussed elsewhere in this chapter, shelter from wind with windbreaks will not always reduce transpiration, indeed the opposite effect has been observed (Carr, 1985). Similarly, the use of shade trees as a drought mitigation measure alone can rarely be justified, since there are so many other, sometimes conflicting, effects of shade on the growth and yield of tea. Portable shade, such as putting a grass mulch on the top of the canopy during extended periods of dry weather, especially in young tea, may sometimes be justified.

Climatic variables

111

(b) Irrigation Over a three year period (1967-1970) the dry-season yield response of mature seedling tea to irrigation in southern Tanzania averaged about 0.8 kg ha- 1 of made tea for each mm of irrigation water applied. With an annual application of about 700 mm, this represented a yield increase of about 500--600 kg ha- 1 on a base yield of around 1000-1200 kg ha- 1 (Carr, 1974). For a high yielding clone (maximum yield> 4000 kg ha- 1), the corresponding yield response to irrigation was about 2 kg ha- 1 mm- 1 (Carr, 1971b). These values were relatively consistent from year-to-year. By contrast, the results of a similar experiment in Malawi at the same time, also with seedling tea, and with the same sequence of cool dry, warm dry, warm wet seasons, the response to irrigation in some years was only 0.3 kg ha- 1 mm-I, but in others matched that obtained in southern Tanzania (Carr et al., 1987). This difference in yield response to irrigation between the two sites was explained on the basis of the high daily maximum temperatures (up to 35-36°C) and, in particular, the associated large saturation deficits of ambient air (> 2.3 kPa) often recorded during September, October and November in Malawi, but not in Tanzania (Fig. 4.3). These adverse climatic conditions would be sufficient to restrict shoot extension rates, even if the soil had just been irrigated, in the same way that low temperatures limited the response to irrigation at both sites during the cool, dry winter months. It has been found with other crops that an increase in the saturation deficit of the air surrounding the leaf can increase transpiration without a commensurate increase in photosynthesis rates, which leads to a reduction in transpiration efficiency (Turner, 1986). Whether or not this applies directly to tea is uncertain, in part due to the sometimes conflicting results reported on how the stomata of tea respond to increases in the saturation deficit of the air. Some work suggests that stomatal conductances are virtually independent of the SD (e.g. Squire, 1978; Callander and Woodhead, 1979) whilst others indicate that stomata are particularly sensitive to changes in SD, closing as the air gets drier (e.g. Carr, 1977a). The conflict may be due to the differences in measurement technique used (porometry, energy balance studies and infiltration liquids), and/or to the types of tea being studied. The issue is also confused by the uncertainty about how changes in stomatal conductance influence photosynthesis (Squire and Callander, 1981) and indeed the importance of current photosynthesis to yield. Conventional wisdom at the moment suggests that the yield of tea is sink limited (not enough shoots) rather than source limited (not enough photosynthates) (Tanton, 1979). What is not in doubt, although it has not really been adequately quantified in tea, is that water stress, reflected in reductions in shoot water potential below about -0.7 to -0.8 MPa, will have an

112

Climate, weather and the yield of tea

immediate and direct effect on rates of shoot extension, which is a major determinant of current yield (Squire and Callander, 1981). The positive response of shoot growth to mist irrigation in areas where dry air is a constraint is confirmation of this (Tanton, 1982b). Considering the depth to which tea roots can penetrate, the limiting soil water deficit (SWD) above which yields are reduced is relatively small. In southern Tanzania the value for deep (4.5 m) rooting mature seedling tea growing in a sandy clay loam soil, with a total available water capacity of 300--400 mm, was 100-150 mm for the season as a whole, but on individual occasions during the year was perhaps less than this (Carr, 1974). For adjacent clonal tea (clone 1), the limiting SWO was probably closer to 50 mm than 150 mm, at least in the warm dry season (Carr, 1971b). The corresponding minimum shoot water potentials at these limiting deficits were about -0.8 MPa (Carr, 1971a). More recent work at the same site, where peak Ecrop rates are 3--5 mm day-I, has confirmed that the value of the limiting SWO probably changes during the dry season, depending on the composition of the shoot population, particularly the proportion of inherently 'fast growing' shoots (Stephens and Carr, 1989). Using the concept of a 'water stress index', based on the summation of daily potential SWO above different base values, they showed that the limiting SWD (for yield) varied during the dry season from 20 to 300 mm. Over the season as a whole, it averaged 100 mm in 1986 (influenced by frost) and 40 mm in 1987 (a more typical year). By comparison the limiting SWD for water extraction appeared to be about 60 mm. These values only represent about 15--20% of the 'extractable' water in the root zone. The same experiment has shown that the yield response to irrigation and rainfall (minimal) over the dry season was linear with values ranging from 1.9 to 2.9 kg ha- I mm- I depending on the level of fertilizer applied (Stephens and Carr, 1989). These values are 2-4 times more than those recorded for seedling tea earlier, reflecting in part the larger maximum yields obtained (up to 4900 kg ha- I of made tea in the third year of the experiment at the optimum level of fertilizer applied, 375 kg N ha- I; Stephens and Carr, 1991a). For planning purposes, it is perhaps better to consider the expected yield loss due to drought on a year-to-year basis. This can be done by using a simple water balance to calculate the potential soil water deficit over the dry season (SWD = Ecrop - rain). Thus in southern Tanzania the reduction in yield below the potential (4000--4500 kg ha- I) will be about 200-250 kg ha- I (100 mm SWOt l in high input (300 + kg N ha- I) systems. By contrast, the corresponding value for low (100 kg N ha- I) input systems, with potential yields of 1500-2000 kg ha-t, is about 100-150 kg ha- I (100 mm SWOtl. An analysis of this sort will allow actual yields to be predicted, with and without irrigation, and a cost-

Climatic variables

113

benefit analysis to be attempted. Care must be taken when extending these values to areas where low temperatures (high altitude areas) or large saturation deficits (Malawi) may restrict responses to irrigation (Palmer-Jones, 1976). For example, the loss of yield due to drought at a high (2200 m) altitude site in Kericho, Kenya has averaged about 400 kg ha- 1 per year (range 0--600 kg ha- 1) out of a maximum yield over a 15 year period of 2000 kg ha- 1 . This represented a yield loss of only about 130 kg ha- 1 (100 mm SWDt 1, largely as a result of low ambient mean air temperatures (16-17°C) (Othieno et al., 1991). Estimating the benefits and worthwhileness of irrigation is not easy, and must be considered on an individual case basis. Account must of course be taken of water availability, costs of water storage and supply and irrigation equipment, and all recurrent costs, as well as the increased revenue from larger yields. There are though ancillary advantages which are sometimes difficult to quantify in purely financial terms. These include improved crop distribution during the year, and the resultant more efficient use of transport, factories, labour and management. In areas where regular dry seasons of three to six months duration occur annually, with potential soil water deficits in excess of 300 mm, irrigation of mature tea is worth considering, providing there are no other major limiting climatic or cultural factors. Shallow soils with low water holding capacities, and young tea must be considered separately. 4.3.7 Wind Very little work has been reported on the effects of wind on the growth and yield of tea, apart from some work done in southern Tanzania by Carr (1971a, 1985). Contrary to expectations at the time, he found that 3-6-year-old clonal tea plants sheltered from wind by 4 m high Hakea sa ligna hedges experienced greater water stress than plants which were more exposed to the wind during extended periods of dry weather, as indicated by shoot water potential measurements (Carr, 1971a), estimates of stomatal opening, measured soil water deficits, visual appearance and yield (Fig. 4.5; Carr, 1985). This unusual response was explained on the basis of the relative changes in the ratio of the canopy (rc) and aerodynamic (ra) resistance to the diffusion of water vapour during the dry season, an analysis based on the data reported by Callander and Woodhead (1979). Providing the adverse effects of drought during the dry season were not excessive, wind-sheltered tea outyielded wind exposed tea during the main growing season, and during the cool weather (Fig. 4.5); tea which had been pruned at the start of the dry weather also refoliated more quickly in the lee of the wind-break. These effects could be

114

Climate, weather and the yield of tea

wind a) rainfed 400 N'

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explained by the influence of I-2°C increases in day-time air temperatures in the sheltered areas on rates of shoot extension where the mean daily air temperatures were only 17-1S0C in the main growing season, and very close to the base temperatures for tea at 13--14°C in the winter months. The work was carried out in a cool, high altitude (1900 m) area at latitude So 36'S; wind speeds were not excessive usually averaging 0.5-2.5 m S-l at 0.15 m above the canopy, or 100-200 km day-1 at 2 m above ground level. Wind direction was relatively constant for most of the year. The results indicate the complexity of interpreting what at first appeared to be a relatively simple study. Shelter from wind is likely to be beneficial in areas where the mean air temperature is less than 17-1SoC, or perhaps where there is advection of hot dry air. There can though be adverse effects of shelter during extended periods of dry weather unless crops are irrigated. Benefits need to be large to cover the cost of maintaining live hedges spaced 40-50 m apart in fields, and the loss in production from the ground occupied by the hedges. Shelter from trees planted between fields in the direction of the prevailing wind is likely to be the best approach where high winds are considered to be a problem, but hedges may still be useful on wind-exposed ridges.

115

Commercial yields

COMMERCIAL YIELDS: CASE STUDIES IN EASTERN AFRICA

Kerlcho

0022'S, 3S021'E alt. 2180 m

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Figure 4.6 Location of sites for commercial case studies in the major tea growing areas of eastern Africa.

4.4 COMMERCIAL YIELDS: CASE STUDIES IN EASTERN AFRICA Long-term yield records from commercial estates in Kenya, Tanzania and Malawi have recently been compared and analysed (Fig. 4.6). The three locations differ in terms of (a) latitude, with the associated seasonal effects, (b) altitude, (c) rainfall amount and distribution, (d) duration of the dry season, (e) temperature, and (f) the saturation deficit

116

Climate, weather and the yield of tea

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of the air. At each location the results of experiments were available to assist in the interpretation of some of the data. The seasonal yield distribution (Fig. 4.7) varies considerably between these three sites, primarily as a result of seasonal changes in temperature and the development of large soil water deficits during the dry season (Fig. 4.8). Kericho in Kenya has the most even yield distribution with only a relatively small drop in production during the dry season. By contrast, both Mufindi, Tanzania and Mulanje, Malawi show marked seasonal variations in yield distribution. For instance, in Mulanje about 80% of the annual yield from unirrigated tea may be harvested during the five months from December to April. In Mufindi, the October peak in yields is due to irrigation. The yields in these areas are now discussed in more detail. 4.4.1 Kenya Yields from two estates in the Kericho district (0° 22' S; 35° 21' E) have been compared. This is the principal tea growing area in Kenya, close to the equator and covers an altitude range of 1700 to 2300 m. Large scale development began in the mid-1930s in cleared, high-altitude rain

117

Commercial yields

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118

Climate, weather and the yield of tea

forest. The soils are deep, red freely draining friable clays (Scott, 1962). The headquarters of the Tea Research Foundation is situated at the northern end of the district (altitude 2178 m), close to one of the two estates (Sambret) which is at an altitude of 2100-2300 m (Monkhouse, 1979). The other estate (Kapgwen) is about 23 km to the south at an altitude of 1840 m. Both estates were planted with predominantly Assam-type seedling tea. Yields have been compared for the IS-year period, 1971 to 1985. On Kapgwen Estate, average yields from 250 ha of tea have increased at an annual rate of about 120 kg ha- 1 of made tea, from 2500 kg ha- 1 in 1971 to around 4000 kg ha- 1 in 1985 (Fig. 4.9). These yields include all fields regardless of their stage in the four-year pruning cycle. This rapid rate of increase follows the removal of shade trees during the 1970s, changes in fertilizer application rates (including the introduction of NPK compound fertilizers during the 1960s, the use of herbicides in place of hand weeding, and routine applications of zinc). There have also been changes in harvesting policies over this time, from predominantly two

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Commercial yields

119

leaves and a bud during the 1970s to mainly three leaves and a bud at present. 'Scheme plucking', where pluckers are allocated individual blocks on an annual basis, was introduced during the late 1980s in some fields. Essentially the same changes in management and cultural practices have been applied to Sambret estate (324 ha) over this time (they are both owned by the same company). There has been barely any increase in yield here though and yields in 1985 were less than those achieved in 1971 (Fig. 4.9). The yield differential between the two estates has increased from 800 kg ha- 1 to 2000 kg ha- 1 over the same time. Both estates are subject to hail damage. These differences in absolute yields, and in rates of change over time have obvious important commercial implications in terms of such issues as profitability, setting of production and budgeting targets, motivation of management and labour, and the justification of expensive inputs, like nitrogen fertilizer. There are also individual company and national issues relating to the need to identify where new tea schemes in Kenya should be developed. In short, it would clearly help managers and planners if it was possible to identify the reasons for (a) the yield differences between the two estates and (b) the year-to-year variability in yield around the long-term trend on both estates. In the Kericho district as a whole, an important variable is altitude: average yields from 21 individual estates tend to decline with increasing altitude (as measured at the estate office) above 1700 m, and especially at altitudes above 2200 m (Fig. 4.10). Sambret estate is above· this upper limit. This influence of altitude can be interpreted through its effect on temperature, and hence on the number of shoot replacement cycles which can be expected in a year. Assuming a lapse rate of 0.6°C for each 100 m increase in altitude (Barry and Chorley, 1976), and a thermal time requirement of 475 datC, above a base of 12.5°C (mean air temperature), the length of the shoot replacement cycle increases from 60-70 days at altitudes between 1500 to 1800 m up to around 120 days at 2200 m, where the main air temperature is only 4°C above the base temperature (Fig. 4.11). The number of shoot generations per year to be expected (assuming water availability is not limiting) can therefore range from ~7 at 1700 m down to only three at 2200 m. These differences are enough to explain the 200 kg ha- 1 reduction in yields (in 1984/85) for each 100 m increase in altitude from 1500 m to 2000 m, and rather more at altitudes above this. Similar analysis of the year-to-year variability in yield highlighted two important factors: one is the duration of the principal dry season, which can last from December to March but is very variable from year to year. The other is the incidence of hail, and the degree of damage to foliage which results. In the Kericho district of Kenya the dry season is warm,

120

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121

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Institute of Tanzania, close to the escarpment edge, and also of the Ngwazi Tea Research Unit 20 km away, where the average annual rainfall is only about 950 mm. Since 1955 annual yields of made tea have increased from only 500--600 kg ha- 1 (across the whole of the 250 ha Kilima estate) in 1955 up

126

Climate, weather and the yield of tea

to 2500 kg ha- 1 in 1985 (Figure 4.14). By 1990 some estates in Mufindi were yielding more than 3000 kg ha- 1 . The most rapid increase occurred during the 1970s averaging about 100 kg ha- 1 y-l. Cultural practices which have changed during the last 20-30 years include the removal of shade trees, weed control with herbicides (allowing the control of couch grass), irrigation (which began in 1971 on a small scale), increased applications of nitrogen (as NPK), a switch to harvesting a higher proportion of three leaves and a bud, limited planting of new clones, and more recently the introduction of scheme plucking. Alongside these changes have been concurrent changes in local financial and national economic management, some of which have not always made operating a commercial company profitably particularly easy. Despite this record yields continue to be obtained way above those considered possible only 20 years ago. Step-wise regression analysis of the yield variability from year-to-year for 220 individual fields suggested that 80% of the variation in yield could be explained by a 'technology' time trend. It was not possible to isolate statistically the influence of individual variables, but positive yield responses to nitrogen fertilizer (as NPK) up to 250-300 kg N ha- 1 were evident (Stephens et al., 1988), values which correspond well with those from a long-term fertilizer experiment in the district. The introduction of irrigation in the 1970s has also had a big effect on productivity. Although potential soil water deficits reach 500-600 mm (in 6 years out of 10), average annual applications of irrigation only total 200-300 mm. Since the yield response to water (at high levels of inputs) is the order of 2-2.5 kg ha- 1 mm- 1 (Stephens and Carr, 1991b), there is the potential to increase yields further (by 400-1000 kg ha- 1), through the application of additional water. Potential yields from existing tea are probably 4500-5000 kg ha- 1 of made tea. 4.4.3 Malawi

Results from a similar but less complete analysis of long-term commercial yield data at Mulanje (16° OS'S; 35° 36' E; altitude 650 m) in southern Malawi highlight other factors influencing long-term yield trends. Here the local climate is dominated by the proximity of the 3000 m high Mulanje mountain. The sequence of seasons is similar to that for southern Tanzania, but the low altitude means that it is much warmer than Mufindi. Rainfall declines with distance from the mountain averaging about 2300 mm at points close to the mountains and declining to 1500 mm 3--5 km away. As a result tea is only grown in a narrow band less than 10 km wide around the base of the mountain. Figure 4.15 illustrates how annual yields from seedling tea planted in 1955 increased at an average annual rate of about 90 kg ha- 1 in the

Commercial yields

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following 30 years to 2800 kg ha- 1 in 1985. This is in response to similar technological changes to those which have occurred in Kenya and Tanzania. By contrast on a neighbouring estate, yields from seedling tea planted in 1916 remained relatively static over the period 1940 to 1970. However, following replanting in 1972 with clonal tea, and the introduction of irrigation, yields have increased at an annual rate of about 300 kg ha- 1 to more than 4000 kg ha- 1 in 1985. By 1990 these fields were yielding 6500 kg ha -1. After allowing statistically for the time trend in yields, and for the stage in the pruning cycle, there was a linear relationship between the dry season yields (from 1976 to 1986) and the corresponding maximum soil water deficit for each of three estates (Fig. 4.16). This corresponded to a mean yield reduction of about 1.2 kg ha- 1 (below 1000 kg ha- 1) for each mm increase in the soil water deficit from 100 to 650 mm, a value which compares with 1.4 kg ha- 1 mm- 1 in Kericho, Kenya and 1-2.9 kg ha- 1 mm- 1 in southern Tanzania. It is important to remember that the saturation deficit during the hot dry season in Mulanje, Malawi may often exceed 2.3 kPa, limiting the response to irrigation in some years.

128

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Climate, weather and the yield of tea

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4.4.4 Summary These comparisons in yield trends over time at three contrasting locations in eastern Africa highlight a number of issues of commercial and scientific interest. In all cases it has been difficult to isolate the effects of individual technological or management changes on production. We are essentially dealing with long-term steady increases in yields which are the result of the combined effects of a number of positive (and negative) changes in cultural and management practices. The rate of increase does though vary from as little as 40 kg ha- 1 y-l at a high (2200 m) altitude estate in Kenya, where low temperatures dominate any improvement in bush management, up to 300 kg ha- 1 y-l for replanted and irrigated polyclonal tea in Malawi at an altitude of only 600 m. Elsewhere yield increases from mature seedling tea have been between 90 and 120 kg ha- 1 y-l. Annual yields averaged across pruning cycles, for individual estates now range from below 2000 kg ha- 1 up to more than 4000 kg ha- 1 of made tea, with individual fields or clones yielding more than this. These differences in yields between sites and over time

Commercial yields

129

can be explained in part by the four factors listed in the introduction of this chapter. (a) The amount of solar radiation received at each site Despite the differences in latitude the annual totals are similar at Kericho and Mufindi averaging about 67 and 65 TJ ha- 1 (TJ = 1012]) respectively, and are about 10% larger in Mulanje (74 TJ ha- 1). The removal of shade trees everywhere over the last 20 years means that all this radiation now reaches the surface of the crop canopy. (b) The amount of solar radiation intercepted by the crop canopy Given full crop cover this will be similar (> 95% at all sites) after bushes have recovered from pruning. Bushes on a three-year pruning cycle will probably intercept less light than those on a four-year cycle; the rate of recovery from pruning will also depend on prevailing temperatures, and the level of water stress at the time of pruning. There are also now fewer bush vacancies than there used to be, and less damage to bushes in the process of hand weeding, following the introduction of herbicides and the use of compound fertilizers. All these factors will have increased the amount of light intercepted by leaves, so that it is now close to the maximum on well managed estates. (c) The efficiency of conversion of intercepted radiation to dry matter Without measurements of total dry matter production at each site it is difficult to separate this variable from any change in the harvest index (see (d) below) which may also have occurred. Improved nutrition and, on some estates, the introduction of irrigation will have increased the efficiency of conversion of intercepted radiation to dry matter. The effects of low (and high) temperatures and large saturation deficits of the air on this variable are not yet fully understood, but all could reduce photosynthesis and dry matter production. Values of the conversion coefficient for most existing tea cultivars appear to be low by comparison with other crops. (d) Partitioning of dry matter to the useful product This will have been influenced by any changes in harvesting policies, particularly a switch from plucking predominantly two leaves and a bud to a larger proportion of three leaves and a bud. The introduction of scheme and, in some places, programmed plucking may have also improved the harvest index, following an increase in shoot size, because

130

Climate, weather and the yield of tea

fewer leaves are left on the bush or broken back, and because fewer small shoots are now removed. Low temperatures, due to altitude or season, drought and large saturation deficits, which all restrict the rates of shoot extension, will probably act to reduce the harvest index, unless the values are extreme enough also to reduce rates of photosynthesis and dry matter production in the same proportion. Little is known about how climatic factors influence the third component of yield, namely

shoot number.

4.5 CONCLUSIONS What can now be added to the conclusions of earlier reviews on the effects of climate and weather on the yield of tea? The main conclusions of the review by Carr (1972) cited at the beginning of this chapter still seem generally to be valid. The role of temperature in controlling shoot extension rates is now better understood: the base temperature for shoot growth is probably in the range 12-13°C, but there is some evidence of considerable clonal variation (7-15°C). This is sufficient to allow clones to be selected for the capacity of shoots to extend at low temperatures. Growth rates seem to be linear with clonal variations in the slope of the response, up to mean daily temperatures of 26-30°C, unless saturation deficits exceed about 2.3 kPa, when shoot extension will be restricted, probably due to a reduction in the turgor or pressure potential of the shoot. The effects of maximum temperatures above 30-35°C have been difficult to separate from any concurrent changes in the saturation deficit, but it is likely that air or leaf temperatures frequently in excess of 35°C will reduce shoot growth rates, as well as perhaps photosynthesis. Thermal time seems to offer a useful way of predicting the length of a shoot replacement cycle, with 475 day °C (above a base of 12.5°C) being accepted, for the moment anyway, as a realistic total for a bud released from apical dominance to grow into a shoot with three leaves and an unopened terminal bud. More work needs to be done to test under what conditions the relationship holds, and to see whether indeed it can be transferred with success to other ecological areas, and for other genotypes. In the meantime though the concept provides a rational basis for comparing the yield potential of different locations, for explaining seasonal differences in crop flow, and for developing harvesting policies based on objective criteria. Soil temperatures still appear to be an important variable, with a lower limit of about 20°C, at 0.3 m under short grass (or 16°C beneath a canopy tea), below which shoot extension rates will be reduced. The corresponding upper levels are 29°C and 25°C respectively. A canopy of tea is light saturated at about 700-800 W m- 2 , which is close to full sunlight in 'winter' months

Acknowledgements

131

or 75% of full sunlight in the 'summer' or rainy season. This level of radiation only becomes excessive if leaf temperature (and/or leaf-to-air saturation deficits) exceed the previously defined limits. It is only under these conditions that shade may be beneficial for tea. Otherwise the expectation is that the conversion efficiency of this radiation will be in the range 0.6 to 1.2 g Mr 1 of photosynthetically active radiation (about 50% of total solar radiation), depending on location (temperature?) and clone. Water stress appears to restrict shoot extension rates at relatively low levels (shoot water potentials < -0.8 MPa), with reductions in yields at potential soil water deficits in the range 20-300 mm, the exact value depending on the proportion or total number, of actively growing shoots within the population. Yield losses due to drought are in the range 1.3 to 3.0 kg ha- 1 mm- 1 increase in the potential soil water deficit above a value of 40-100 mm. The higher values refer to high input, large (3000-4000 kg ha- 1) yielding crops. Minimum annual rainfall totals are 1150-1400 mm, unless irrigation is available. Hail is still potentially very damaging with annual yield losses of up to 30% (average 10%) experienced in vulnerable areas of Kenya. Shelter belts are probably only useful in areas where the mean air temperature is below 17-18°C, or where advection of hot dry air can be expected. Following this increased understanding of how climate and weather influence the development and yield of tea, the next stage is to attempt to model the effects of these variables on the principal growth processes in order to predict potential and actual total yields in different locations, and yield distribution during the year. A predictive interpretation of the effects of weather on yields would also allow the next generation of clones to be selected against established criteria, such as the capacity to grow at low temperatures, to tolerate dry air conditions, or to withstand droughts with minimum damage. Removing the tea bush from its natural habitat and exporting it around the world has provided producers and scientists with many challenges. Fortunately there is a great deal of genetic variability which remains to be exploited, and all for the sake of a 'nice cup of tea'! ACKNOWLEDGEMENTS Recent research work reported here has been supported by the United Kingdom Overseas Development Administration, the Tanzania Tea Authority and Brooke Bond Tanzania Ltd and the Mufindi Tea Company Ltd. We thank them and also Brooke Bond Kenya Ltd, the LujeriiSayama Group and Esperanza Estates for the provision of commercial yield data, and the Directors and staff of the Tea Research Institute of Tanzania and the Tea Research Foundations of Kenya and Central Africa for their willing cooperation.

132

Climate, weather and the yield of tea

REFERENCES Allen, J. C. (1976) A modified sine wave method for calculating degree days. Environmental Entomology,S, 388-96. Barry, R. G. and Chorley, R. J. (1976) Atmosphere, Weather and Climate, 3rd edn, University Paperbacks, London. Barna, D. N. (1970) Light as a factor in the metabolism of the tea plant, in Physiology of Tree Crops (eds L. C. Luckwill and C. V. Cutting), Academic Press, New York, pp. 307-22. Blackie, J. R. (1972) Hydrological effects of a change in land use from forest to tea plantation in Kenya. lASH/UNESCO Studies and Reports on Hydrology, 12, 312-29. Blackie, J. R. (1979) The water balance of the Kericho catchments. East African Agriculture and Forestry Journal, 43, 55--84. Callander, B. A. and Woodhead, T. (1979) Eddy correlation measurements of sensible heat flux, and estimation of evaporative heat flux, over growing tea. East African Agriculture and Forestry Journal, 43, 85-101. Callander, B. A. and Woodhead, T. (1981) Canopy conductance of estate tea in Kenya. Agricultural Meteorology, 23, 151-67. Carr, M. K. V. (1970) The role of water in tea crop, in Physiology of Tree Crops (eds L. C. Luckwill and C. V. Cutting), Academic Press, New York, pp. 287-305. Carr, M. K. V. (1971a) The internal water status of the tea plant (Camellia sinensis): Some results illustrating the use of the pressure chamber technique. Agricultural Meteorology, 9, 447-60. Carr, M. K. V. (1971b) An assessment of some results of tea-soil-water studies in Southern Tanzania, in Water and the Tea Plant (eds M. K. V. Carr and Susan Carr), Tea Research Institute of East Africa, Kericho, pp. 21-48. Carr, M. K. V. (1972) The climatic requirements of the tea plant: A review. Experimental Agriculture, 8, 1-14. Carr, M. K. V. (1974) Irrigating seedling tea in Southern Tanzania: effects on total yields, distribution of yield and water use. Journal of Agricultural Science (Cambridge), 83, 363-78. Carr, M. K. V. (1976) Methods of bringing tea into bearing in relation to water status during dry weather. Experimental Agriculture, 12, 341-51. Carr, M. K. V. (1977a) Changes in the water status of tea clones during dry weather in Kenya. Journal of Agricultural Science (Cambridge), 89, 297-307. Carr, M. K. V. (1977b) Responses of seedling tea bushes and their clones to water stress. Experimental Agriculture, 13, 317-24. Carr, M. K. V. (1985) Some effects of shelter on the yield and water use of tea, in Effects of Shelter on the Physiology of Plants and Animals. Progress in Biometeorology (ed. J. Grace), vol. 2, Swets and Zeitlinger B. V, Lisse, pp. 127-44. Carr, M. K. V. and Carr, Susan (eds) (1971) Water and the Tea Plant, Tea Research Institute of East Africa, Kericho. Carr, M. K. V., Dale, M. O. and Stephens, W. (1987) Yield distribution in irrigated tea (Camellia sinensis) at two sites in Eastern Africa. Experimental Agriculture, 23, 75--85. Carr, M. K. V., Stephens, W. and Congdon, T. C. E. (1988) Tea in Tanzania. Outlook on Agriculture, 17, 18-22.

References

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Clowes, M. St J. and Starch, P. (1988) Sayama irrigation trial. Tea Research Foundation (Central Africa) Quarterly Newsletter, (92), 6-10. Cooper, J. D. (1979) Water use of a tea estate from soil moisture measurements. East African Agriculture and Forestry Journal, 43, 102-21. Corley, R. H. V. (1983) Potential productivity of tropical perennial crops. Experimental Agriculture, 19, 217-37. Dagg, M. (1970) A study of the water use of tea in East Africa using an hydraulic lysimeter. Agricultural Meteorology, 7, 303-20. Fordham, R. (1970) Factors Affecting Tea Yields in Malawi, PhD Thesis, Bristol University. Fordham, R. (1971) Stomatal physiology and water relations of the tea bush, in Water and the Tea Plant (eds M. K. V. Carr and Susan Carr), Tea Research Institute of East AFrica, Kericho, pp. 89-100. Fordham, R. (1977) Tea, in Ecophysiology of Tropical Crops (eds P. de T. Alvim and T. T. Kozlowski), Academic Press, New York, pp. 333-49. Grice, W. J. (1982) The formulation of workable plucking policies. Tea Research Foundation (Central Africa) Quarterly Newsletter, (68), 7-17. Hadfield, W. (1968) Leaf temperature, leaf pose and productivity of the tea bush. Nature (London), 219, 282-4. Hadfield, W. (1974a) Shade in North-east Indian tea plantations I. The shade pattern. Journal of Applied Ecology, 8, 151-78. Hadfield, W. (1974b) Shade in North-east Indian tea plantations II. Foliar illumination and canopy characteristics. Journal of Applied Ecology, 8, 179-99. Kingdon-Ward, F. (1950) Does wild tea exist? Nature (London), 165, 297-9. Laycock, D. H. (1964) An empirical correlation between weather and yearly tea yields in Malawi. Tropical Agriculture (Trinidad), 41, 277-91. Laycock, D. H. and Wood, R. A. (1963) Some observations on soil moisture use under tea in Nyasaland. Part I. The effect of pruning mature tea. Tropical Agriculture (Trinidad), 40, 35-42. Lebedev, G. V. (1961) The tea bush under irrigation. (In Russian). Izvestia Akadamia Nauk SSSR, Moscow. Magambo, M. J. S. (1977) Canopy characteristics of seven clones of tea (Camellia sinensis L.) estimated by the use of inclined point quadrats. Tropical Agriculture (Trinidad), 54, 205-12. Magambo, M. J. S. and Cannell, M. G. R. (1981) Dry matter production and partition in relation to the yield of tea. Experimental Agriculture, 17, 33-8. McCulloch, J. S. G. (1965) Tables for the rapid computation of the Penman estimate of evaporation. East African Agricultural and Forestry Journal, 30, 286-95. Mkwaila, B. (1987) A comparative observation of shoot growth in Mulanje and Thyolo. Tea Research Foundation (Central Africa) Quarterly Newsletter, (87), 13-15. Monkhouse, A. J. W. (1979) The commercial development of Sambret estate. East African Agriculture and Forestry Journal, 43, 51-4. Monteith, J. L. (1977) Climate and the efficiency of crop production in Britain. Philosophical Transactions of the Royal Society of London, B281, 277-94. Obaga, S. 0., Squire, G. R. and Langat, J. K. (1988) Altitude, temperature and the growth rate of tea shoots. Tea, 9(1), 28-33.

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Othieno,

c.

O. (1975) Surface run-off and soil erosion in fields of young tea.

Tropical Agriculture (Trinidad), 52, 299-308.

Othieno, c. O. (1978a) Supplementary irrigation of young clonal tea in Kenya. I. Survival, growth and yield. Experimental Agriculture, 14, 229-38. Othieno, c. O. (1978b) Supplementary irrigation of young clonal tea in Kenya. II. Internal water status. Experimental Agriculture, 14, 309-16. Othieno, c. O. (1982) Diurnal variations in soil temperatures under tea plants. Experimental Agriculture, 18, 195--202. Othieno, C. O. (1983) Effect of weather on the recovery from pruning and yield of tea in Kenya. Journal of Plantation Crops (Supplement), 44-52. Othieno, C. O. and Ahn, P. M. (1980) Effects of soil mulches on soil temperatures and growth of tea plants in Kenya. Experimental Agriculture, 16, 287-94. Othieno, C. o. and Laycock, D. H. (1977) Factors affecting soil erosion within tea fields. Tropical Agriculture (Trinidad), 54, 323-9. Othieno, c. 0., Stephens, W. and Carr, M. K. V. (1991) Yield variability at the Tea Research Foundation of Kenya. Agricultural and Forest Meteorology (in press). Owuor, P.O., Obaga, S. O. and Othieno, c. O. (1990) The effects of altitude on the chemical composition of black tea. Journal of the Science of Food and Agriculture, 50, 9-17. Palmer-Jones, R. W. (1976) Estimating irrigation response from data on unirrigated crops. American Journal of Agricultural Economics, 58(1), 85--7. Ranganathan, V. and Natesan, S. (1985) Potassium nutrition of tea, in Potassium in Agriculture (ed. R. D. Munson), Agronomy Society of America, Madison, pp. 981-1022. Renard, c., Flemal, J. and Barampama, D. (1979) Evaluation of the resistance of the tea bush to drought in Burundi. (In French) Cafe Cacao The, 23, 175--82. Sakai, S. (1975) Recent studies and problems of photosynthesis of tea plant. Japan Agricultural Research Quarterly, 9, 101--6. Scott, R. M. (1962) Summary of soil survey observations on Sambret valley. East African Agriculture and Forestry Journal, 27, 22. Shaxson, T. F. (1971) Making better use of rain, in Water and the Tea Plant (eds M. K. V. Carr and Susan Carr), Tea Research Institute of East Africa, Kericho, pp. 177--89. Squire, G. R. (1977) Seasonal changes in photosynthesis of tea (Camellia sinensis L.). Journal of Applied Ecology, 14, 303-16. Squire, G. R. (1978) Stomatal behaviour of tea (Camellia sinensis) in relation to environment. Journal of Applied Ecology, 15, 287-30l. Squire, G. R. (1979) Weather, physiology and seasonality of tea (Camellia sinensis) yields in Malawi. Experimental Agriculture, 15, 321-30. Squire, G. R. (1985) Ten years of tea physiology. Tea, 6(2), 43-8. Squire, G. R. and Callander, B. A. (1981) Tea plantations, in Water Deficits and Plant Growth (ed. T. T. Kozlowski), vol. 6, Academic Press, New York, pp. 471-510. Stephens, W. and Carr, M. K. V. (1989) A water stress index for tea (Camellia sinensis). Experimental Agriculture, 25, 545--8.

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135

Stephens, W. and Carr, M. K. V. (1990) Seasonal and clonal differences in shoot extension rates and numbers in tea (Camellia sinensis). Experimental Agriculture, 26, 83--98. Stephens, W. and Carr, M. K. V. (1991a) Responses of tea (Camellia sinensis) to irrigation and fertiliser: 1. Yield. Experimental Agriculture, 27, 177-91. Stephens, W. and Carr, M. K. V. (1991b) Responses of tea (Camellia sinensis) to irrigation and fertiliser: II. Water use. Experimental Agriculture, 27, 193--210. Stephens, W., Hamer, P. J. c. and Carr, M. K. V. (1988) The yield response of tea to irrigation and fertilizer. Second Annual Report to ODA: 1986-87, Silsoe College, Silsoe. Stephens, W., Othieno, C. O . and Carr, M. K. V. (1991) Climate and weather variability at the Tea Research Foundation of Kenya. Agricultural and Forest Meteorology (in press). Stigter, C. J., Othieno, C. O. and Mwampaja, A. R. (1984) An interpretation of temperature patterns under mulched tea at Kericho, Kenya. Agricultural and Forest Meteorology, 31, 231-9. Tanton, T. W. (1979) Some factors limiting yields of tea (Camellia sinensis). Experimental Agriculture, 15, 187-92. Tanton, T. W. (1982a) Environmental factors affecting the yield of tea (Camellia sinensis) I. Effects of air temperature. Experimental Agriculture, 18, 47-52. Tanton, T. W. (1982b). Environmental factors affecting the yield of tea (Camellia sinensis) II. Effects of soil temperature, day length and dry air. Experimental Agriculture, 18, 53-63. Templer, J. C. (1971) Experience of some soil conservation measures at the Uganda Station of the Tea Research Institute of East Africa, in Water and the Tea Plant (eds M. K. V. Carr and Susan Carr), Tea Research Institute of East Africa, Kericho, pp. 171-5. Turner, N. C. (1986) Crop water deficits: A decade of progress. Advances in Agronomy, ~, 1-51. van der Laan, J. 'to (1971) Irrigation of tea in East Pakistan, in Water and the Tea Plant (eds M. K. V. Carr and Susan Carr), Tea Research Institute of East Africa, Kericho, pp. 113--25. Willat, S. T. (1970) A comparative study of the development of young tea under irrigation. 1. Establishment in the field. Tropical Agriculture (Trinidad), 47, 243--9. Willat, S. T. (1971) A comparative study of the development of young tea under irrigation. 2. Continued growth in the field. Tropical Agriculture (Trinidad), 48, 271-7. Willat, S. T. (1973) Moisture use by irrigated tea in Southern Malawi. Ecological Studies, 4, 331-8.

CHAPTER 5

Soils C.

o. Othieno

5.1 INTRODUCTION It is considered (Mann, 1935) that among tropical crops, there is none which demands more precisely than tea, a soil with special characters if

economic yield is to be obtained. Tea is however, grown in a wide range of soil types and therefore it does not mean that tea will grow economically on only a few soils. What it means is that there are certain soil characteristics which must be met by any particular soil where tea is to be grown. This chapter describes these soil characteristics which are essential for successful economic growth of the tea plant. 5.2 FORMATION AND TYPES OF TEA SOILS Tea is grown in a wide range of soil types found in tropical, sub-tropical and temperate climatic conditions (Mann, 1935; Child, 1953; Harler, 1971; Eden, 1976). These soil types have developed from diverse parent rock material and under different climatic conditions. In China, Indonesia, Sri Lanka, south India, Turkey and Georgia (USSR) tea is mostly grown on sedimentary soils derived from gneiss or granite. In north-east India, except in Darjeeling, tea is grown on flat alluvial lands which occupy the vast area of the Brahmaputra Valley in Assam. Peat (bheels) soils which have been drained are successfully used in Cachar to grow tea. But in Kyoto and Kanaya, the main areas of Japanese tea, the crop is grown on soil types derived from volcanic ash and in Taiwan, tea occupies a tract of tertiary rocks derived from a residual formation. Most of the soil types of Kenya, Uganda, Burundi, Rwanda, Tanzania and Congo have developed from volcanic ash. However, tea is also grown on soils derived from gneiss and granite in these countries. Malawi's tea is Tea: Cultivation to consumption Edited by K. C. Willson and M. N. Clifford © 1992 Chapman & Hall, London. ISBN 0412338505

Sub-tropical areas: Central Africa: Malawi (Mulanje) Taiwan: Kilung North India: Assam Cachar Darjeeling China: Zhejiang Yunnan Japan: Kyoto Kanaya Turkey: Rize USSR-Georgia (Chakwa)

Tropical areas: Kenya: Kericho Uganda: Rwebitaba Tanzania: Usambaras Mufindi Indonesia: West Java Sri Lanka: Kandy Nuwara Eliya South India: Coonoor Annamalais (Cinchona)

88° 12'E 120° E 105° E 136° E 138° E 40° 30'E 43° 30'E

21'E 26'E 37'E 05'E E E 45'E 40'E 45'E

26° 55'N 30° N 18° N 35° N 34° 30'N 41° N 42° 15'N

35° 30° 38° 35° 110° 81° 80° 76° 76° 35° 35'E 121° E 94° 12'E

22'S 39'S 08'5 30'S N N N 15'N 15'N

Longitude

16° 05'5 24° N 26° 47'N

0° 0° 05° 08° 7° 8° 7° 11° 10°

Latitude

2233

1590 1933 2085 1850 2050

2100 1450 1800 1950 3500 2375 2255 2135 3500 10.5 14.4 15.6 18.3 6.0 0.6 2.8 5.0 5.0 6.7 -5.6

14.5 17.0 17.5 13.2 22.2 22.8 13.3 15.6

Annual Lowest rainfall month (Oe) (mm)

30.0 28.3 28.9 28.9 16.7 25.0 27.2 26.7 25.6 22.3 26.1

17.0 19.0 22.5 18.0 22.8 25.8 15.6 21.1

(Oe)

Highest month

20.0 21.1 22.1 23.3 11.1 12.8 15.6 15.6 15.0 14.0 15.0

15.8 18.0 20.0 15.6 22.5 23.9 14.4 18.4

(Oe)

Mean

19.5 13.9 13.3 10.6 11.7 24.4 24.4 21.7 20.6 15.6 31.7

2.5 2.0 5.0 4.8 0.6 3.0 2.3 5.5 5.5

(Oe)

Difference between highest and lowest

Table 5.1 Mean annual rainfall and lowest and highest mean month temperatures in tropical and sub-tropical tea growing areas of the world

0-15 15-90 90-125

7.55 2.18 1.41

1.53 1.38 0.53

4.4 4.4 4.6 4.9 4.7 4.6

3.00 2.66 5.40

8.46 8.00 7.09 3 .68

5.30 4.15 4.00

5.10 4.50 4.60 4.75

1.66

Total

0.28

0.09 0.08 0.40

0.17 0.14 0.33

0.60 0.58 0.50 0.19

0.10

N(%)

9.90 10.00 7.80

10.50 11.46 9.63

8.20 8.02 8.24

10.05

ClN (ratio)

22 4 3

1.50 1.00 0

14 14 24

14 8 7 4

15

Available P (ppm)

0.51 0.45 0.19

0.15 0.15 0.16

1.16 0.69 0 .36

2.08 1.90 1.74 3.08

0.96

K

1.125

2.46

0.90 0.60 0.20 0.46

0.78

Ca

1.73 8.83 1.40 4.24 1.48 3.54

0.08 1.71 0.07 0.41 0.16 0.10

1.31

2.50 1.40 0.70 2.01

0.35

Mg

Exchangeable bases (meq/100 g)

Source 1, Dey (1969); 2, Othieno (1973); 3, Sandanam et al. (1978); 4, Chu (1975); 5, Ranganathan (1976).

South India (Anamallais)

II III

I

0-23 0-23

0-5 5-10 10-15 0-23

4.73

(%)

1:2.5)

(em)

0-30 (Fallow)

Organic matter

pH (soil water

Soil depth

General chemical properties of some tea soils

Malawi (Newly planted tea) (Replanted tea) Sri Lanka Taiwan Horizon

Kenya (Kericho)

India (Assam)

Country (area)

Table 5.2

0.30 1.05 4.9

18.50 18.50 0.53

1.0 3.9 3.8

Exchangeable H(meq/lOO g)

11.2 10.4 10.4

18.50

2.70

20.78

5.83

5 5 5

4 4 4

1 1 3

2 2 2 1

1

CEC Source (meq/lOO g)

140

Soils

grown on soil types that have been washed from a granite massif and on sedimentary gneissic soil types. Despite the diversity of soil types on which tea is grown, all the soils have been formed under or exist in high rainfall conditions as this is the most important climatic factor for successful tea growing. Consequently, the soils have been formed under special type of weather (permanent moist conditions) combined with intensive leaching of the products of weathering. The degree of leaching and hence the character of the resulting soil depends not only on the rainfall but also on the temperature. Because of differences in temperature, soils formed in tropical climates are likely to have certain characters different from those formed in the sub-tropical or semi-tropical conditions. The tea areas in tropical climates experience minimal temperature variations as compared with those in sub-tropical climates as shown in Table 5.1. The mean temperature in the warmest month of the year does not differ greatly in the two climatic classes except that caused by elevation, such as between Kericho in Kenya at 2178 m above mean sea level and West Java in Indonesia at 550 m above mean sea level. On the other hand the mean temperatures in the coolest month differ greatly in the two classes. In the formation of the soils, there are conditions of permanent moist soil, which in tropical regions is exposed continually to a moderately high and uniform temperature. In sub-tropical regions, the temperatures are variable and in some places like Georgia in USSR go below the freezing point of water. However, all these soils have one thing in common, they are acid as tea grows best in acid soils (Table 5.2). 5.3 CLASSIFICATION OF TEA SOILS The diversity of soil types on which tea is grown successfully makes it very difficult to have the soils fit in a general classification. This is further complicated with the existing different descriptive terms and systems used in soil classification around the world. Nevertheless, most of the tea soils in southern India are classified as latosols (Ranganathan and Natesan, 1985) while those in Bangladesh, China, Sri Lanka and Taiwan are red-yellow podzolic and reddish-brown lateritic. In northeast India in Assam, the soils are alluvial and in Darjeeling they are sedimentary types whereas in Cachar, bheel or peaty soils are found (Mann and Gokhale, 1960). In Indonesia tea soils are classified as andosols. The soils in USSR are podzolic and those of Japan are redyellow podzolic and volcanic. In Kenya and parts of Tanzania and Uganda, most of the soils are volcanic (Scott, 1962; Othieno, 1973a, Carr, 1974) which are classified as nitisols in the FAO-UNESCO classification system (Sombroek et al., 1982). However there are pockets of acrisols and ferrasols on which tea is grown in the East African countries.

Chemical properties

141

5.4 IDENTIFICATION THROUGH INDIGENOUS VEGETATION Use of certain indigenous vegetation (indicator plants) which grow successfully in soils where tea has established successfully has helped in indicating suitability of a soil for tea. All the indicator plants associated with areas suitable for tea growing require high and well distributed rainfall and intensively weathered and leached soils. The most reliable indicator plants for tea are the aluminium accumulators as classified by Chenery (1955). In India and Sri Lanka Albizzia species have been found to be good indicators for suitability of a soil for tea. Mann (1935) points out that in north India, i.e. Assam, Darjeeling and Duars, A. stipulata, A. lebbeck, and A. procera, respectively are the best indicator plants and in Sri Lanka A. moluccana is a good indicator plant. In Georgia in USSR A. julibrissim has been associated with good tea soils. In Kenya (Brown, 1966) a number of indigenous species have been associated with good tea soils. These are: trees - Newtonia buchanani, Albizzia sp: shrubs - Vernonia auriculifera, Triumfetta macrophylla; Herbs - Boreria princei; ferns Pteridium aquilinum (bracken). In Uganda, Dissotis violacea, D. brazzaei, D. irringiana and Craterispermum laurinum have been used in identifying tea soils. 5.5 CHEMICAL PROPERTIES The basis of mineral soils is clay. There are different types of clay mineral depending on the original parent rock material from which it is derived. However, the structure of all clay minerals consists of layers of silica-aluminium oxides and hydroxides. Each layer is attached to the next layer by hydrogen bonding. A simple basic chemical formula for a clay mineral (Mg and/or Fe which are constituents of some of the clay minerals not included) is: XzAlySiwOv(OH)u nH20: where subscripts are number of moles. The predominant clay mineral found in most tea soil is kaolinite which consists of 1:1 silica-aluminium layers. However some soils have certain amounts of illite and montmorillonite clays which consist of 2:1 silicaaluminium layers. Clays have charged absorption sites represented by X in the above formula, capable of absorbing and releasing ions in an exchange reaction for similar positively or negatively charged ions, i.e. ion exchange. The most common positively charged ions which can be absorbed and exchanged with similarly charged ions are called cations and are Ca 2+, Mg2+, K+, Na+ and Nm. The most common negatively charged anions

142

Soils

are: sof-, CI-, N0 3, H2Pof- and HCO}. Added to the basic chemical properties of clay minerals are organic compounds in varying amounts which form part of any given soil particle. Table 5.2 gives general chemical properites of some tea soils. 5.5.1 Acidity The main causes of soil acidity are hydrogen (H»fH) and aluminium (AI3 »fH) Ions. (a) Leaching (hydrogen ion) In an intensively leached soil in which tea grows best, most of the ions especially the cations (calcium, magnesium, potassium) are replaced by hydrogen from the water molecule and can be washed off the mineral. The reaction may be shown simply as follows:

Soil particle

Soil particle

The result of the reaction shown on the diagram above is a hydrogensaturated soil particle. This is the main source of acidity in tea soils. (b) Aluminium ions Aluminium ions on their own or when they react with water also produce acidity according to the following reaction, especially in acid soils of below pH 5.5. A13+ + 3H20 ~ Al (OHh + 3H+ (c) Other sources of acidity

Nitrogenous fertilizers Nitrogenous fertilizers, especially most of those used in tea, are acid producing. When ammonium nitrogen fertilizer such as sulphate of ammonia is added to the soil, the ammonium ion replaces base elements of potassium on the exchange sites of clay minerals. The replaced bases are leached out and the ammonium ion on the soil particles is nitrified a process which produces acidity. The simplified process is as follows: (i)

143

Chemical properties 2NH! + 302 2N02: + O2

~

~

2N0 2 + 2H20 2N0 3

+ 4H+

In addition to direct uptake of the NH! ion by the tea plant (Ishigaki, 1984), only a small fraction between 30 and 40% of the nitrate formed in the above reaction is utilized by plants arid about 10-20% is lost by denitrification. The remainder, between 40 and 50%, is leached beyond the rooting zone along with an equivalent amount of bases leaving the soil acid (Ranganathan and Natesan, 1987).

Organic acids In the process of decomposition of organic matter, a number of organic acids which supply hydrogen ions are released into the soil. The ions exchange with and release bases on the clay minerals. The released bases are subsequently leached out leaving the soil acid. (ii)

(d) Soil pH requirement for tea and liming It is generally agreed that the optimum range of soil pH for the tea plant is 5.0 to 5.6. This optimum varies with the nature of the soil, particularly the organic matter content. Soils of pH 6.5 and above are always considered unsuitable for tea and even those above pH 5.6 require correcting with acid material such as aluminium sulphate or elemental sulphur before tea is planted, e.g. Flemal (1960). On the lower end of the scale tea grows in as Iowa pH as 4.0 or below. Its preference for acid soils has been mistaken in the past to mean dislike for calcium, i.e. calcifuge (Thomas, 1941). Indeed, calcium is the third highest nutrient in a mature tea leaf after nitrogen and potassium. Mann (1935) in India and de Haan and Schoo reI (1940) in Indonesia have shown that tea plants can grow well in soils with over 0.5% calcium. On the other hand, Mann (1935) points out that 'the presence of a small trace of

lime, at least in the form of carbonate seems almost fatal to the tea plant as a commercial crop'. Carpenter et al. (1925) conducted an experiment in the use of lime in acid soil in Assam. Three-year-old tea was treated with various amounts of lime. After 5 years, the heavily limed seemed to have suffered and the whole area was replanted with plants 1 year old. After 2 further years, growth assessments as shown in Table 5.3 were recorded. In East Africa, Willson (1967) gave results which showed that calcium applied to the soil, either in a nitrogenous fertilizer (calcium ammonium nitrate) or as gypsum put in the tea planting-hole in the hope that baseexchange would result in a reduction of the potassium content in a potassium rich soil (Hutsite), was deleterious to the yield of mature tea or growth of the young plant. Similar deleterious effects have recently

144 Table 5.3

Soils Effect of liming on growth of tea plants

Treatment No. 1 2 3 4 5 6 7

Amount of lime (Ca2 C03 ) added (tonnes ha- 1 ) Assessment Nil 3.57 7.14 10.70 14.72 21.41 28.54

Good tea Good tea but poorer than No.1 Poor tea. Clearly worse than No. 2 Distinctly poorer tea Still poorer tea Very bad tea Very bad tea indeed very little growth

Further trials using quick lime (CaO) in corresponding quantities gave similar results. Source: Carpenter et al. (1925).

been repeatedly observed in Kenya (Wanyoko, unpublished and Lang'at, personal communication) . The adverse effect of excess calcium has also been demonstrated by Prillwitz (1932) . The observed deleterious effects of excess calcium were attributed to the disturbance of the balance between the amounts of the available bases in the soil. If tea can grow in soils with over 0.5% (5000 ppm) calcium (de Haan and Schoorel, 1940), is it correct to refer to it as calcifuge? On the other hand, if a trace of lime as calcium carbonate is almost fatal (Mann, 1935), is it the carbonate form of calcium which tea does not like? But lime as calcium carbonate is being used in tea in south and north-east India. These questions need answers before tea nutrition and soil acidity can be adequately understood. 5.5.2 Hutsites or high pH soils Hutsites is a term used exclusively in East Africa to describe areas, in otherwise good tea land, where tea is unable to establish well because of too high base nutrient contents especially potassium and calcium, i.e. high pH. These areas were previously used, either as homesteads or, the worst patches, as cattle kraals. In East Africa, such soils are acidified by using sulphur, aluminium sulphate or ammonium sulphate, a technique based on work reported by Willson (1966). (a) Sulphur Sulphur acidifies soil relatively quickly and experiments have shown that it improves the rate of growth of tea bushes very considerably. Sulphur is not soluble in water, so it must be broken up and distributed evenly over a depth of soil. Sulphur is easily crushed to a

Chemical properties

145

sufficient fineness by spreading the commercial lumpy material on a hard floor and rolling a heavy concrete culvert section or similar object over it. The sulphur should not be ground in any type of mechanical mill as it will catch fire. For field planting, sulphur must be thoroughly mixed with the soil from the planting holes before it is returned to the holes. The quantity of sulphur required depends on the pH, as follows (TRFK, 1986).

Soil pH values Sulphur per hole (g) 5.9 - 6.4 115 225 6.5 - 6.9 340 7.0 - 7.4 450 7.5 and higher (b) Sulphate of ammonia This chemical acidifies soil quickly. However, experiments have shown that if it is mixed with soil before planting it reduces the rate of growth of tea, both stumps and potted plants, and has even been known to kill plants. Therefore, it is not recommended for the improvement of areas prior to planting. (c) Aluminium sulphate This chemical will acidify soil without adverse effects on tea. It is very soluble in water and easily available as it is used for purifying water supplies. A weight of 450 g of aluminium sulphate has the same effects as 115 g of sulphur. (d) Treatment of tea established on hutsites In hutsite areas, where tea is growing but not thriving, the best treatment is to apply aluminium sulphate: 450 g m- 2 placed on the ground every 3 months for a year is usually adequate. The chemical should be spread as evenly as possible. The commercial material is usually in the form of large, very hard lumps and breaking these is difficult, but they dissolve quickly in soil moisture. It is sometimes possible to buy the 'kibbled' grade of aluminium sulphate, this is preferable as it has been broken down to small pieces. Sulphur should not be applied as a surface dressing to sites already planted with tea. Sulphate of ammonia is beneficial as it acidifies the soil in addition to providing nitrogen. However, very large quantities are needed to reduce the pH of hutsite soils quickly. It is quicker and cheaper to use

146

Soils

aluminium sulphate to reduce the pH and to use sulphate of ammonia purely as a nitrogen source. In most cases where tea has been established using sulphur or aluminium sulphate as described above no problems arise later. The reduction of pH due to leaching usually ensures that the tea roots are able to continue growing outside the treated soil of each planting hole. A further safeguard is to apply nitrogen as sulphate of ammonia. Occasionally the tea roots will not grow into untreated soil, and as a result growth is slowed down and plants may die when they have been in the ground for about a year. This usually happens where the pH initially has been very high. When the initial pH is over 7.0, the pH of the untreated soil between planting holes should be measured 6 months Table 5.4 Treatment of high pH soil for nursery use*

Sulphur addition (gm- 3 ) Maximum

Minimum pH

5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7.0

Sulphur Minimum time between treatment and planting (weeks)

60 115 170 225 285 340 395 450 510 565 620 675

1 2 3 4 5 6 7 8 9 10 11 12

Sulphur Minimum time between treatment and planting (weeks)

60 115 170 225 285 340 395 450 510 565 620 675 735 790 845 900 960 1015 1070 1125

1 2 3 4 5 6 7 8 9 10 11 12 13

14 15 16 17 18 19 20

* Adapted from Tea Growers Handbook, 1986 (TRFK, Kenya).

Chemical properties

147

after planting. If it is over 6.5, the whole area should be treated with aluminium sulphate, 450 g m- 2, with applications at 3-monthly intervals until tests show that the pH is below 6.0. For nursery use, the soil must be mixed with the maximum quantity of sulphur given in Table 5.4 and left for at least the minimum time before cuttings are planted. 5.5.3 Liming

In south India where 26% of all the tea soils have pH between 4.0 and 4.5 and 5% of the soils with pH less than 4.0, use of lime to bring the pH to about 5.0 is recommended as follows (Ranganathan and Natesan, 1987):

Soil pH Quantity of lime (CaC0 3 ) to add (tonnes ha- 1) Below 4.0 3 2 4.0 to 4.5 1 4.6 to 4.9 5.5.4 Nutrient requirements (See also Chapter 9, pp. 269-90)

In addition to oxygen, hydrogen and carbon which are obtainable in air and water (carbon as carbon dioxide [C0 2 ]), tea, like any other plant, requires many other nutrients for its growth. It has been found that many species of green plants require the same nutrients, although different amounts of each. The nutrients required by all the green plants (Table 5.5) have been grouped together and referred to as essential nutrients. (Ranganathan, 1979). Three of these are those already mentioned, i.e. oxygen, hydrogen and carbon. The remaining thirteen are mineral nutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (5), manganese (Mn), zinc (Zn), copper (Cu), iron (Fe), boron (B), molybdenum (Mo) and chlorine (Cl). Aluminium (AI) has been found to be an essential nutrient for tea (Kinoshi, et al., 1985). (a) Principal or macro-nutrients Of the essential nutrients mentioned above, the first nine are considered principal or major nutrients as they are required in relatively larger amounts than the rest. Oxygen, hydrogen and carbon are readily available in the air or water and hence need no specific consideration but the remaining six need consideration.

+ 4)

*After Ranganathan (1979).

Amount removed (1

Total assimilated

4 Wood 200

80

120

2 Mature foliage

3 Branchlets and twigs

100

(%)

Proportional dry weight

6.0

11.0

2.0

1.1

3.9

4.0

N

0.98

1.65

0.48

0.24

0.43

0.50

P

2.4

3.7

0.4

0.4

0.9

2.0

(%)

K

1.1

3.1

0.5

0.16

1.5

0.6

Ca

0.55

1.07

0.30

0.16

0.36

0.25

Mg

8

24

4

4

12

4

Zn

7

20

4

4

9

3

B

8

24

4

4

12

4

Cu

Nutrients assimilated and removed by tea (% dry weight and ppm)*

1 Flush (crop)

Part

Table 5.5 Mn

35

90

15

15

40

20

130

590

45

280

180

85

(ppm)

Fe

200

420

100

100

120

100

Al

12

33

6

6

15

6

CI

23

42

15

10

9

8

Na

Chemical properties

149

(i) Nitrogen In addition to its role in the formation of protein, nitrogen forms an integral part of the chlorophyll molecule. An adequate supply of nitrogen is associated with vigorous vegetative growth and a deep green colour. A stunted-yellow appearance is indicative of nitrogen deficiency. Because of the frequent removal the harvestable portion of tea crop which is the tender succulent shoot (two leaves and a bud) and the necessity to prune the plants frequently so as to generate new vigorous shoots to produce the required crop, demand for nitrogen is very high compared with other plants. Plants generally are able to utilize either nitrate (N03) or ammonium (NH"4) ion. However, tea is thought to prefer the latter as shown by work done in Japan (Ishigaki, 1974). Soils are capable of supplying quantities of both ions to sustain a forest vegetation which is not harvested until many years of growth in the case of timber. But for tea, the amounts supplied by a soil mainly derived from organic matter or humus cannot sustain commercial rate of growth and hence the necessity for use of nitrogen fertilizers (see Chapter 9, p. 271). It is estimated that harvestable crop contains between 3.5 and 5.0% nitrogen on dry matter basis. This is equivalent to annual removal of between 70 and 100 kg N ha- 1 for low yielding tea of 2000 kg made tea ha -1 and for high yielding tea of 5000 kg made tea ha- 1 year- 1 the annual removal is between 175 and 250 kg N ha- 1 . Phosphorus Phosphorus is required by plants because it plays a key role in the DNA which is the energy house of the plant and is essential in the plant's reproductive system. However, the latter is not essential for commercial tea as the harvestable part is vegetative. It is generally considered that plants absorb most of their phosphorus in the ionic form of H 2P04. This ionic form of phosphorus readily reacts with oxides/hydroxides of iron and aluminium, which are abundantly available in acid soils, to form insoluble compounds (Sivasubramaniam and Talibudeen, 1972; Othieno, 1973; Battacharyya and Dey, 1983). Therefore the phosphorus availability in acid soils is a subject of wider agricultural interest. Fortunately the tea plant's requirement for this nutrient is very small compared with other principal nutrients. It is estimated that harvestable crop of tea growing in a soil well supplied with phosphorus is between 0.20 and 0.25% P on dry weight basis. The annual removal for tea yielding 2000 kg made tea ha- 1 year- 1 is between 4 and 5 kg P ha- 1 and for tea yielding 5000 kg made tea ha- 1 year- 1 it is between 10 and 12.5 kg P ha- 1 . In the soil phosphorus is derived from the decomposition of rocks containing the mineral apatite and also from organic matter. (ii)

150

Soils

(iii) Potassium

In terms of the relative amount required by the tea plant, potassium is second only to nitrogen. While nitrogen and phosphorus are synthesized into compounds necessary for the growth of the plant, potassium is used by the plant mainly in the production and translocation of carbohydrates. It is considered to be intimately related to nitrogen metabolism. This is important in tea where large amounts of nitrogen fertilizers are sometimes used without corresponding relative amounts of potassium. It is generally taken up by plants in the ionic, K+ form. The harvestable tea crop contains an average 1.75 to 2.00% K on a dry weight basis which works out to between 35 and 40 kg K ha- 1 and between 87.5 and 100 kg K ha- 1 being removed each year for tea yielding 2000 and 5000 kg made tea ha -1 year-I, respectively. In the soil potassium is derived from minerals such as feldspars, biotite and muscovite and also from the decomposition of organic matter. Soil factors of prime importance and direct relevance in potassium availability and its nutrition of plants are soil physical properties, type and content of clay mineral in a soil, potassium dynamics (K adsorption, fixation and release), ion exchange and soil pH (Sivasubramaniam and Talibudeen, 1971; Ranganathan and Natesan, 1985). (iv) Calcium

Problems with calcium in tea nutrition are discussed under pH. Despite the problems, it is worth mentioning here that in terms of relative amounts of nutrients taken up by the tea plant, calcium is third to nitrogen and potassium. Therefore a considerable amount of this nutrient is required by the tea plant. Calcium is required by plants for the growth of the apical meristems and formation of seed in the case of seed bari plants. On average the harvestable crop contains between 0.5 and 1.0% Ca dry weight basis which works out to between 10 and 20 kg Ca ha -1 being removed annually from fields of tea yielding 2000 kg made tea ha- 1 year-I. For high yielding fields of 5000 kg made tea ha- 1 year- 1 the removal is between 25 and 50 kg Ca ha- 1 year-I. In the soil calcium is derived from the decomposition of rocks containing calcium such as limestone. (v) Magnesium

Although required in relatively smaller amounts than calcium, magnesium perhaps ranks third, after nitrogen and potassium, in terms of importance for economic growth of the tea plant. It is the only mineral constituent of the chlorophyll molecule which is responsible for photosynthesis. Magnesium is absorbed by plants as the Mg2+ ion for photosynthesis. It is very mobile within the plant and is readily

Chemical properties

151

translocated from older to younger plant parts in the event of deficiency. The magnesium deficiency leaf syndrome of a dark V-shape surrounded by yellow is well known in the lower foliage. Magnesium is a primary constituent of most clay minerals and rocks containing biotite, dolomite, chlorite and others. On average, harvestable crop contains between 0.05 to 0.25% Mg on dry weight basis, therefore for tea yielding 2000 and 5000 kg made tea ha- 1 year- 1 annual removal is between 4 and 6, and 10 and 15 kg Mg ha-l, respectively.

(vi) Sulphur Sulphur is thought to be connected with the conversion of the sun's radiation into chemical energy in the photosynthesis process. Sulphur is required in relatively small amounts by tea and it is usually taken up by the plants as SO~- ion. The harvestable crop contains between 0.15 and 0.20% of sulphur on dry weight basis. Most of the nitrogenous fertilizers used in tea contain sulphur, therefore the deficiency is not always encountered except in isolated cases where sulphur deficient soils may be used in nurseries for propagation purposes. Such cases have been reported in Malawi, i.e. the 'sulphur yellows' syndrome occurs where sulphur deficiency arises in young nursery plants which show general yellowing (Harler, 1971). Much of the soil sulphur is derived from organic matter, humus and soil minerals. (b) Trace or micro-nutrients The remaining seven elements known to be essential for plants for their growth are only required in very small amounts and hence are referred to as trace or micro-nutrients. These are manganese, zinc, copper, iron, boron, molybdenum and chloride. Of these only zinc and copper are of general interest in most tea growing areas of the world. Low levels of soil available boron which cause concern have been experienced in north-east India (TRA, 1979/80). (i) Zinc

Zinc is a constituent of the enzyme systems that regulate various plant metabolic activities. Zinc deficiency has been found to reduce the growth of tea and was first recognized in Sri Lanka, and has since been confirmed in other parts of the world (Tolhurst, 1973). Foliar application of zinc as explained in Chapter 9 (p. 288) corrects the deficiency.

Copper In a limited localized area of Malawi shortage of copper in the leaf has been observed and since the enzyme which oxidizes the leaf in the (ii)

152

Soils

fermentation process is a copper-protein compound, the tea grown in such areas will not ferment (Harler, 1971; Clowes and Mitini-Nkhoma, 1987).

(iii) Boron Boron is required by plants in extremely small amounts. Boron regulates metabolism of carbohydrates and water-soluble amino compounds in plant tissue. It is also thought to be related to calcium and potassium metabolism. The element is weakly held as an anion on the soil exchange complex where it is readily leached by large amounts of water passing down the soil profile. It is therefore a trace element which is likely to limit tea yields. In a trial using potted plants at Tocklai, applied boric acid was negatively correlated with the uptake of calcium by the tea plants (TRA, 1979/80). (c) Evaluation of soil fertility for tea Soil fertility evaluation, to assess the quantity of nutrients available to plants, can be done by chemically analysing either soil or plant or both. The principle behind the analysis is to relate the soil nutrient availability to the plants' need or uptake. Two of the commonly used practical soils tests for evaluating plant nutrient needs of the tea plant are the determination of soil pH and its capacity to hold cations. pH is measured in soil-water mixtures, usually 1:1, 1:2 or 1:2.5 The capacity of a soil to hold cations, referred to as cation exchange capacity (CEC), is a direct measure of the quantity of base nutrients available in the soils which is very important. The CEC of a soil is measured by washing (leaching) or replacing (exchanging), the held base elements with a salt usually ammonium salt and then determining the ammonium held after washing. Ammonium acetate solution is commonly used to replace cations in acid soils (see Table 5.6).

(i) Chemical analysis of soil Soil consists of an extraordinarily complex chemical mixture of different mineral and organic substances. Therefore the success of soil analysis for fertility assessment depends on securing a representative soil sample plus subsequent careful handling operations. After obtaining and preparing a representative sample the next step is the extraction of the nutrients or their determination. Whatever the extraction method used, the assumption is that what is extracted with whatever extractant is considered to be what is available for extraction by roots. Extractable 'available' nutrients are those held loosely on exchange sites on clay mineral or organic matter. Several extractants and extraction methods are available. However, the most important factor is that whatever

153

Chemical properties Table 5.6

Analytical methods for soils

Element

Extractant

Analytical technique

1 M ammonium nitrate solution 1 M ammonium nitrate solution

Flame emission spectrometry Atomic absorption spectrometry

Kjeldah digestion with PhosphoriC/Sulphuric acids in conjunction with a catalyst Sodium bicarbonate solution

Titration of liberated ammonia with 0.1 M hydrochloric acid

Organic carbon

1 M ammonium nitrate solution Walkey-Black

Cation exchange capacity

1 M ammonium acetate leaching

Flame emission spectrometry Titration with ferrous ammonium sulphate Ammonium ion concentration determined titrimetrically

Total exchangeable bases pH

1 M Ammonium acetate leaching

Calcium Magnesium

Total nitrogen

Phosphorus

Potassium

Soil/Water 1:2.5

Solution spectrophotometry after complexing with vanadomolybdate reagent

Flame emission/atomic absorption spectrophotometer pH meter

method is used it should be simple and give reproducible results in relation to nutrients extraction by roots. Table 5.6 gives commonly used and recommended chemical analytical methods for tea soils.

Plant analysis Plant tissue analysis is a more direct and unique way of assessing soil fertility by the use of growing plants (Jackson, 1960; Chapman and Pratt, 1961). When used in combination with soil chemical analysis it can be of tremendous benefit in the assessment of soil fertility and the giving of advice on fertility use especially with perennial crops like tea. Plant analysis has been used widely by various laboratories to assess fertility of tea soils (de Haan and Schoorel, 1940; Jayaraman, 1950, 1951; Oniani, 1964; Pritula, 1967; Akhmelov and Bairamov, 1968; Lin, 1969; Willson, 1969; Ranganathan, 1970; Tolhurst, 1972). Table 5.7 gives commonly used and recommended plant tissue analytical methods.

(ii)

154

Soils

Table 5.7 Analytical methods for plant tissue samples

Element

Digestion method

Calcium

Digestion of ash in concentrated hydrochloric acid Digestion of ash in concentrated hydrochloric acid Digestion of ash in concentrated hydrochloric acid Low temperature drying and ashing (in presence of calcium hydroxide) followed by digestion with 6 M hydrochloric acid Digestion of ash in concentrated hydrochloric acid Digestion of dried material in concentrated nitric/perchloric acid Digestion of ash in concentrated hydrochloric acid Digestion of ash in concentrated hydrochloric acid Kjeldahl digestion with phosphoric/sulphuric acids in conjunction with a catalyst Acid treatment of dried material followed by ashing and digesting in concentrated hydrochloric acid

Magnesium Manganese Boron

Copper Molybdenum Iron Zinc Nitrogen

Phosphate

Potash

Digestion of ash in concentrated hydrochloric acid

Sulphate

Cold water

Aluminium

Digestion of ash in concentrated hydrochloric acid

Analytical technique Flame emission spectrometry Atomic absorption spectrometry Atomic absorption spectrometry Solution spectrophotometry after complexing with carminic acid Atomic absorption spectrometry Solution spectrophotometry Atomic absorption spectrometry Atomic absorption spectrometry Titration of liberated ammonia with 0.1 M hydrochloric acid Solution spectrophotometry after complexing with vanadomolybdate reagent Flame emission spectrometry Solution spectrophotometry of the precipitated barium sulphate Atomic absorption spectrometry using a nitrous oxide flame

Physical properties

155

5.6 PHYSICAL PROPERTIES In terms of plant production the physical properties of a given soil include soil depth, textural composition of the mineral soil, organic matter, their structural arrangement or aggregates which include porosity and water-holding capacity of the soil. 5.6.1 Soil depth An ideal tea soil is that which is deep and well drained with a minimum 'available depth' of say, two metres (Mann, 1935; Mann and Gokhale, 1960). It is however known that tea is grown in high water-table soils and other types of shallow soils which occasionally include drained swamps. These soils are however problematic and require special management attention if tea is to give economic yields. It is vitally important, if tea soil selection is to be done with any confidence that a soil profile pit, at least 2 m deep, be dug in representative sites and the various soil horizons examined for their suitability for tea planting. To illustrate the importance of available soil depth, take for example two soils of similar physical properties with water-holding capacity of 20 cm m- I except that one has 1 m and the other 2 m of available depth. The shallow soil would have 20 cm as compared with 40 cm of water after heavy rainfall or irrigation and drainage of excess water. When the two soils are subjected to an extended period without rain or irrigation, tea grown in the shallow soil will suffer first. 5.6.2 Texture The tea plant will thrive on soil of nearly any texture. Othieno (1973a), Chu (1975), Eden (1976) and Ranganathan (1976) have given textural composition of soil types in some tea growing countries. Some of these are given in Table 5.8. From the table it is noted that tea grows on soils of varying textural composition. In Taiwan tea is grown in soils with both high and low clay contents. Ideal soil texture for tea in the Assam area of north-east India is thought to be sandy loam (Mann and Gokhale, 1960) but tea is grown successfully on soils with texture grades ranging from fine sand to heavy clays in the same area. In peaty (bheel) soils of Surmah Valley (Cachar), tea is grown in silty loam soils with over 30% organic matter. The best tea soils in Kericho District of Kenya have between 75 and 85% clay content of kaolinite type and in some parts of China, Sri Lanka, south India and the Usambaras in Tanzania, tea is grown on very coarse and gravelly soils (personal observations) which are not worthy to be called soils.

A Bramaputrah alluvium, Assam B Peat (bheel) soil, Surmah Valley C Clay flat, Surmah Valley D Anamallais, south India E Nilgiris, south India F Central Province, Sri Lanka G Uva, Sri Lanka

16 34 27 17 6 SaL

A

7 33 11 33 SiL

B

17 43 28 8 SaL

C

21 20 25 20 5.2 SiL 2.13 1.07 51.6 65.5

E

34 33 22 10 SaL

SiL

G

20 19 36 25

F

SaL

24 39 29 6

H

H Pengalengan, Java, Indonesia I Usambaras, Tanzania J Kiambu, Kenya K Kericho, Kenya L Hsing-hua series, Taiwan M Ho-kang series, Taiwan - Data not available

32 18 28 5 3.4 SiL 2.00 1.03 54.3 59.5

D

21 32 10 37 4.2 SaL 2.61 1.23 53 22.5

I

2 6 9 83 6.8 C 2.55 0.77 71.3 60.9

K

14 34 52 2.3 CL 2.71 1.39 48.7 28.2

L

Textual grades SaL Sandy loam SiL Silty loam CL Clay loam C Clay

2 4 11 82 8.5 C 2.60 0.85 73 59.0

J

Physical properties of some tea soils of the world (0--30 cm depth on average)

Texture - Fractions (%) Coarse sand/gravel Fine sand Silt Clay Organic matter Texture grade Particle density Apparent density Perosity (%) Water-holding capacity (%)

Table 5.8

49 30 1.7 1.7 CL 2.66 1.42 46.8 20.8

M

Physical properties

157

Tea planted on gravelly and very coarse sand soils is liable to suffer in a drought although during rainy periods the growth may be satisfactory. On the other hand heavy soils, particularly those of predominantly montimorillonite and illite clay types are difficult to manage especially with regard to proper tilth and drainage: in short a heavy soil of this type is a problem both during periods of excessive rain and no rain. Soils of kaolinitic clays such as those of Kericho in Kenya are free draining and easy to manage. 5.6.3 Soil structure

In their natural condition soils often have their individual particles arranged in clods and crumbs (or peds as they are often referred to). These peds are bonded together by clay particles and organic matter present in the soil. The size distribution of the peds or its converse, the size distribution of the pore space between them determines the soil structure, and in part, the soil tilth (Russell, 1973). Because of the diversity of tea soils, their structures are also diverse but an aggregated or crumb structure with many pore spaces is the ideal structure for an arable soil. A good structured soil should have about 50% pore spaces. The crumb structure of the soil is ensured through (Dey, 1969): (i) active soil fauna, chiefly worms and insects which act upon the undecomposed litter and eventually bind the fine drained soil particles into crumbs through incorporation of humified materials; (ii) masses of ramifying living roots drying out the soils at periodic intervals into crumbs and (iii) decayed roots providing fresh organic matter and channels for the movement of water, thereby making the soil crumbs more stable. 5.6.4 Organic matter

Soil organic matter consists of a whole series of products which range from undecayed plant and animal tissue through well decomposed, fairly stable amorphous brown to black material bearing no trace of the parent material from which it was derived. It is the latter material that is normally defined as soil humus (Russell, 1973). Soil organic matter has many roles. It acts as the binding material joining soil particles to form a stable soil structure. Under natural conditions it is the main source of plant nutrient and home and source of food for soil fauna. Tea soils vary in their organic matter contents ranging from less than 1% in some tropical, high leached soils to over 30% in some peat (bheel) soils (Table 5.2). However, the tea plant once established and well maintained generates a lot of organic matter from leaf-fall and prunings.

158

Soils Table 5.9 Dry matter production and nutrient content of plant

parts formed above pruning cuts of bushes (clone 8/6/60) under regular plucking

Plant part above pruning cut

Cumulative Nutrient removal (kg ha- 1) dry matter N P K (tonnes ha -1 )

Up to first year

Crop Foliage Twigs Wood Total

1.20 3.30 0.82 1.79 7.11

48 122 13

41 224

6 15 2 8 31

24 60 10 15 109

4.80 4.74 3.50 7.02 0.60 20.66

192 164 64 68 13 601

18 12 7 10 2 49

96 46 24 76 11 202

10.80 7.33 6.74 17.27 1.80 43.94

414 249 142 162 61 1028

46 30 25 45 10 166

201 81 81 64 7 412

Up to second year

Crop Foliage Twigs Wood Leaf litter Total

Up to third year

Crop Foliage Twigs Wood Leaf litter Total for the cycle Source: Ranganathan (1985).

Of the 10 to 20 tonnes biomas produced per hectare per year, a large portion of this is returned to the soil in the form of prunings (Table 5.9). Several other physical factors can render a soil to be unsuitable for tea growing even if other factors may not be limiting. A high water-table, i.e. waterlogging is one such factor. This is very important because it is known that tea roots will not grow (Fig. 5.1) when the soil or subsoil is waterlogged for a prolonged period. Therefore a soil which has poor drainage should be avoided. If it is necessary to plant such an area to tea, then a drainage system to a depth of at least 1 m should be provided. It needs to be mentioned here that drainage is not so much for the removal of surface water per se but to bring about conditions in the root environment where there is an adequate supply of oxygen. Indeed tea can grow in swamp soils provided the water in the soil is free flowing and there is an adequate supply of oxygen to the tea roots (personal observation in Burundi).

Physical properties

waterlogged

159

waterlogged

(b)

Figure 5.1

(a) Effect of waterlogging (submerged plants): (i) normal watering, no waterlogging; (ii) roots half submerged for 2 weeks; (iii) roots fully submerged for 2 weeks. b) Effect of waterlogging on root development.

160

Soils

In addition to waterlogging, another physical factor which may render soil unsuitable is an impediment from a hard-pan of clay, murram or rocks. It is clear in Table 5.8 that tea is grown in soils with diverse textural composition. Whether the soil is as murramy or gravelly as those found in parts of China and Sri Lanka respectively there must be adequate available depth. In new areas which are still under natural vegetation, areas with such a hard-pan are easy to identify visually because, more often than not, the area will be covered with shallow rooting plants, i.e. grasses instead of forest vegetation of tall trees. Such areas should be avoided unless it is possiqle to break and open the soil to the required depth for successful tea establishment. 5.6.5 Water-holding capacity The water-holding capacity of a given tea soil and its availability to plants is dependent on soil textural composition, their aggregation

90 .,

80

W

E 70 ::J '0 > 60 >.0

..

,.

.'

0

u

...

Q)

::J

30

iii

'0 20 ::2

10

,

Q)

• •.•..

~

..... ,.

0> • . . . ' "

., . . ',' , c .... . :'.:': . ~ ..... ..

: : ·•..... c : ', ', 0,": ,' •. "0 . . . . .

" ":" a. . .. .. · •. '. : . 0> . • . . • · .... . . c

:::e 0 50 C Q) C 40

. .. . ... . .. . . .

..

.....

• • • .. •

..

.

.!::

~

·

a.

............. ·. .. ... . .. .. ... . . ... .

'u m m

.0

.

••• ••

'.'

. ...

Kericho, Kenya"

~

. . . . . . . .... . ·.. . . ...........

'0

Q)

u::::

·.',

0 2

4

-6

-8

1- 0

:

"

.',

.... . '.

- 12

"

:. :

Marikitanda, Tanzaniat

....

- 14

- 16

• Average waterholding capacity 200 mm m· l at 3 m depth

t Average waterhold ing capacity 111 mm m· l at 2 m depth

Figure 5.2 Soil moisture release curves of two soils with different textures: Kericho, Kenya x-x soil with up to 80% clay, and Marikitanda, Tanzania ------- soil with only 28% clay (average depth of 0-2 m), (After Othieno, 1973a.)

Biological properties

161

(structure) and the rooting depth of the tea plant. The coarser the texture (higher content of coarse material) the less the water-holding capacity (Figure 5.2) (Othieno, 1973b). The less the water-holding capacity the shorter times such a soil will be able to supply water to the tea plant, especially in an extended period without rain or irrigation. 5.7 BIOLOGICAL PROPERTIES Soils are living entities as opposed to inert rock particles because they have a population of micro-organisms living in them. These microorganisms derive their energy by decomposing (oxidizing) organic residues left behind by the plants growing on them or animals feeding on the plants. In the final analysis, the plants growing on the soil subsist on the products of microbial activity, for micro-organisms are continually oxidizing the dead plant and animal remains and leaving behind, in a form available to the plant, a whole range of nutrients. On this concept a fertile soil is that which contains a good balance of microbial activity to sustain a continuous supply of the required plant nutrients. The biologically active agents in soils are: 1. Macroanimals, i.e. rodents such as rats (mole rat is an important rodent of tea) to earthworms which are extremely useful in improving soil structure. 2. Microanimals, i.e. nematodes, which are major pests in some tea areas, and protozoa (amoeba, flagellates). 3. Fungi which include beneficial (decomposition of organic matter) and harmful diseases such as Armillaria mellea and Poria hypoiateritia root rot diseases of tea. 4. Actinomycetes which in terms of population per given volume of soil are second only to bacteria. Actinomycetes undoubtedly are of great importance in respect to the dissolution of soil organic matter and release of plant nutrient therefrom. They are known to reduce even the most resistant compounds such as lignin. 5. Bacteria have the largest, in terms of number, population in any given soil. Bacteria, as a group, almost without exception participate vigorously in all of the organic transactions so vital if a soil is successfully to support higher plants. They not only rival but often exceed both fungi and actinomycetes in this regard. Bacteria are the agents of enzymatic transformations of: (i) nitrification, (ii) sulphur oxidation, and (iii) nitrogen fixation. As with fungi and actinomycetes, bacteria also have harmful (diseases) effects on plants.

The harmful effects, i.e. pests and diseases associated with the soil microbial activities in tea production, are well studied and documented

162

Soils

(b)

Figure 5.3

Soil and water conservation. (a) Microcatchment holding water after a rain-storm. (b) Terrace delivering run-off water into a grassed cut-off drain.

Management of tea soils

163

(Chapters 10 and 11). The beneficial role of the microbes of transforming soil organic matter into plant nutrients, especially in acid tea soil, is however not well understood and so far has not attracted much interest. 5.8 MANAGEMENT OF TEA SOILS Husbandry practices which ensure maintenance of good soil structure and fertility are vital management considerations for any agricultural soil. Because tea is grown in high rainfall areas, in most cases on sloping to steep land, one most important management aspect of tea soils is how they can be conserved for sustainable crop production. The other important management aspect concerns conservation, i.e. better use of little, or disposal of excess, water in areas with marginal rainfall and poor drainage respectively. 5.8.1 Water conservation In marginal rainfall areas, every drop of rain is important for the growth of the plant. Use of catchments (Fig. 5.3) and mulches (Fig. 5.4) for water conservation are therefore essential (Shaxson and Hall, 1968; Othieno, 1980). 5.8.2 Removal of excess water by drainage In the Assam and bheel soils of Cachar tea areas of north-east India and certain swampy or river beds in a number of tea growing countries, high water-tables resulting in frequent water-logging are a major problem. Under such conditions it is essential to provide artificial drainage facilities to drain excess water below the root zone. Provision of an efficient drainage system to a depth of 1m is considered adequate for tea growing areas prone to waterlogging above this depth. 5.8.3 Maintenance of fertility

In addition to the use of fertilizers (see Chapter 9) for the maintenance of soil fertility, husbandry practices which ensure build-up and maintenance of adequate soil organic matter are considered important for sustainable production. (a) Fields of young tea This starts with clearing and land preparation prior to planting. It is important that, whatever methods are used in clearing and preparing

164

Soils

land for tea planting, they should ensure that there is minimum loss of the rich topsoil. This is often a problem when heavy machinery is used in land clearing which tends to scrape and push off the rich topsoil. In addition to careful clearing and land preparation, the foregoing soil conservation measures will help to maintain soil fertility, especially in early stages following planting. (b) Fields of mature tea Table 5.9 gives dry matter production and nutrient (NPK) removed in a 4-year pruning cycle experimental plots in southern India (Ranganathan and Natesan, 1985). At the end of the cycle total cumulative dry matter production was 43.94 tonnes ha-1 (an average of about 11 tonnes ha- 1 of which 10.80 tonnes ha- 1 (an average of 2.70 tonnes ha- 1) was removed as crop. This leaves 33.14 tonnes ha- 1 most of which would be pruned before the beginning of the new cycle. If all this is left in situ, the nutrients returned to the soil would be 614, 100, 211 kg ha- 1 of nitrogen, phosphorus and potassium respectively. Table 5.10 gives 10 years mean yields monthly leaf nutrients, soil pH and organic matter from an experiment conducted in Kericho, Kenya to quantify the effect of removal of prunings (Othieno, unpublished, 1979). The benefits of leaving

Management of tea soils

(b)

Figure 5.4

Use of mulch in tea. (a) Young tea. (b) Three years later.

165

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Soils

Table 5.10 Effects of 10 years' removal of tea prunings on tea yields, leaf nutrients and some soil chemical properties (0-10 em depth)

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... Samples taken at the end of seventh year. Sources: Othieno (unpublished, 1979).

prunings in situ are clearly demonstrated. This has been demonstrated in Malawi also (Grice and Malenga, 1987). Soil and water conservation (a) Soil erosion and control measures Soil erosion is the major cause of decline in soil fertility and hence its ability to give sustainable crop production. In tea areas, water is the major cause of soil erosion. It begins when the raindrops detach and displace or loosen soil particles which are then transported by run-off. Run-off is a result of inability of a soil to accept in-coming rainfall or irrigation water. This could be because the soil is already too wet to hold any more water or the rate (intensity) of the in-coming water is in excess of the rate of infiltration. Also, the soil structure may be poor with very little porosity and/or the land may be too steep to allow water to infiltrate into the soil. Rainfall intensity, soil wetness and land steepness are three major factors which contribute to soil erosion on tea lands. Figure 5.5 shows the relationship between rainfall intensity and run-off, on one hand, and eroded soil on the other hand recorded from an experiment on field of young tea with a uniform slope of 10% in Kenya (Othieno and Laycock, 1977). In further analysis of the data from the experiment quoted above it was observed that in addition to rainfall intensity and run-off, ground cover by mulch, cover crop or tea canopy played a major factor in determining the amount of run-off and soil erosion as given in Fig. 5.6.

Management of tea soils

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168

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Run-off and soil erosion is severe in the early stages of development of" the young tea plants, especially the period between land preparation and the end of the first 2 years of planting. Once the tea plants have developed a uniform ground cover canopy of 60% or above, both runoff and soil erosion become negligible. Therefore, husbandry practices which encourage fast early canopy development such as closer spacing (higher plant density) and planting of easily branching and spreading tea varieties are recommended in addition to the traditional soil conservation measures such as terracing and/or cover cropping and mulching (Othieno, 1980). For detailed recommended practices on soil and water conservation readers are referred to the Handbooks of the Tea Research Foundations of Central Africa (Shaxson and Hall, 1968) and Kenya (TRFK, 1986). Yield data and soil nutrient data generated from an experiment in which some plots had their prunings left in situ and in others removed confirmed the practical benefits of leaving the prunings in situ. It is therefore a good husbandry practice not to remove the prunings (Grice and Malenga, 1987). (b) Effect of herbicide weeding In addition to leaving prunings in situ herbicide weeding of tea results in minimum disturbance of the soil particularly the topsoil where feeder roots are concentrated. This practice not only helps to build-up organic matter and thus soil fertility but also the feeders grow, without the frequent damage which arises from implement weeding, into the nutrient-rich soil media thus ensuring efficient nutrient uptake (Digitarius, 1963; Willson, 1972). 5.9 UPROOTED AND REPLANTED TEA LAND Studies on the management of uprooted and replanted tea areas are still continuing in various tea growing countries and conclusions of these studies are not expected for some time. Nevertheless, there are indications which suggest that when tea is uprooted in land which has been under tea for many years the land should be rehabilitated by planting something else like Guatemala grass in combination with a leguminous plant like Desmodium (Manipura, 1972). Such rehabilitation will help in improving the soil structure and also increase soil fertility. (Templer and Machaga, 1978). It has recently been observed in north-east India (George and Singh, 1989) and Kenya that the old tea land could have developed some toxic (allelopathic) substance during the many years it remained under tea

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prior to uprooting. In Kenya it has been noted that food crops such as maize and beans failed completely to grow and give yields, despite use of fertilizers, when planted in such land immediately following uprooting.

REFERENCES Akhmelov, G. S. and Bairamov, B. I. (1968) Foliar diagnosis of the nutritional status of the tea plant. Fertilite, 30, 5(H)8. Bhattacharyya, N. G. and Dey, S. K. (1983) Role of pH and aluminium on phosphate availability of tea soils. Two and a Bud, 30 (1/2), 61--4. Brown, L. H. (1966) A report on tea growing potential in Kenya, Ministry of Agriculture, Nairobi, Kenya. Carr, M. K. V. (1974) Irrigating seedling tea in Southern Tanzania: Effects on total yields, distribution of yields and water use. Journal of Agricultural Science (Cambridge), 83, 363-78. Carpenter, P. H., Cooper, H. K. and Harler, C. R. (1925) Soil acidity and the use of lime on tea. Quarterly Journal of Scientific Deptartment, Indian Tea Association. Chapman, H. D. and Pratt, P. F. (1961) Methods of Analysis for Soils, Plants and Waters, University of California, Division of Agricultural Sciences, pp. 5(H)4. Chenery, E. M. (1955) A preliminary study of aluminium and the tea bush. Plant and Soil, 6, 174-200. Child, R. (1953) The Selection of Soils Suitable for Tea. Pamphlet No.5, Tea Research Institute of East Africa, Kericho, Kenya. Chu, H. M. (1975) Studies on soil properties and their grading for tea land improvement. Taiwan Tea Experiment Station Bulletin, No. 67, 35-66. Clowes, M. So. J. and Mitini-Nkhoma, S. P. (1987) Copper deficiency on young clonal tea growing close to Mulanje mountain. Quarterly Newsletter, Tea Research Foundation (Central Africa) (88), 13-15. Dey, S. K. (1969) A study of some soils from Assam, Central and East African tea areas. Two and a Bud, 16(2), 65-9. Digitarius (1963) Tea without weeds - a T.R.1. summary. Tea, 3(6), 24-34. Eden, I. (1976) Tea, 3rd edn, Longman, London, pp. 8-16. Flemal, J. (1960) La fumure du theier au Kivu. Bulletin Agricole du Congo, 51(4), 807-32. George, U. and Singh, R. (1989) Biological and chemical factors affecting replanting in tea. Proceedings of the 31st Tocklai Conference, Tea Research Association Tocklai Experimental Station, India. Grice, W. J. and Malenga, N. E. A. (1987) Are your prunings still being stolen? Quarterly Newsletter Tea Research Foundation (Central Africa) (86), 11-12. de Haan, I. and Schoorel, A. F. (1940) Potash deficiency in tea culture (in Dutch with English summary). Archief voor de Theecultur 14, 43-81. Harler, C. R. (1971) Tea Growing, Oxford University Press, London, pp. 34--40. Ishigaki, K. (1984) Influence of aluminium and boron on the growth and content of mineral elements of tea plants on sand culture method. Study of Tea, 66, 33--40.

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Jackson, M. L. (1960) Soil Chemical Analysis, Prentice-Hall Inc. Englewood Cliffs, New Jersey, USA. Jayaraman, V. (1950) Report of the soil chemist, in United Planters Association of South India Annual Report 1950-51, Cinchona, India. Jayaraman, V. (1951) Report of the soil chemist, in United Planters Association of South India Annual Report 1950-51, Cinchona, India. Kinoshi, S., Miyamoto, S. and Taki, T. (1985) Stimulatory effects of aluminium on tea plant growth grown under high phosphorus supply. Soil Science and Plant Nutrition, 31 (3), 361-8. Lin, C. F. (1969) The development of leaf analysis as a guide to fertilization of tea bushes. Soils and Fertilizers, 32, 1085. Mann, H. H. (1935) Tea Soils, Technical Communication No. 32, Imperial Bureau of Soil Science, Harpenden, England. Mann, H. H. and Gokhale, N. G. (1960) Soils of tea growing tracts of India. Journal of the Indian Society of Soil Scientists, 8, 191-200. Manipura, W. P. (1972) Influence of mulch and cover crop on surface run-off and soil erosion on tea lands during the early growth of replanted tea. Tea Quarterly 43(3), 95-102. Oniani, O. I. (1964) Diagnosis of the potassium fertilizer requirement of the tea plant. Fertilite, 21, 20--3. Othieno, C. O. (1973a) Physical characterisation of soils, in Annual Report, Tea Research Institute of East Africa, Kericho, Kenya, pp. 38-4l. Othieno, C. O. (1973b) Effect of organic mulches on yields and phosphorus utilization by plants in acid soils. Plant and Soil, 38, 17-32. Othieno, C. O. (1979) Estimates of removal of N, P and K by a clonal tea plant. Tea in East Africa, 19 (2), 11-13. Othieno, C. O. (1980) Effects of mulches on soil water content and water status of tea plants in Kenya. Experimental Agriculture, 16, 295-302. Othieno, C. O. and Laycock, D. H. (1977) Factors affecting soil erosion on a field of young tea. Tropical Agriculture (Trinidad), 54(4), 323--30. Prillwitz P. M. H. (1932) Bemestingsproeven bij de theecultur. 1. Proeven op jongvulcanische gebergtegronden. Archief voor de Theecultur, 6, 1-32. Pri tula , Z. V. (1967) Diagnostic of the nutrition of the tea plant under the conditions of the Krasnodar region. Soils and Fertilizers, 30, 94l. Ranganathan, V. (1970) Genesis of fertilizer recommendation in tea. Bulletin of United Planters Association of South India Tea Scientific Department, 28, 39-44. Ranganathan V. (1976) Annual Report of the Chemistry Division United Planters Association of South India Tea Scientific Department, Tea Research Institute Cinchona, India, pp. 39-86. Ranganathan, V. (1979) Annual Report of the Chemistry Division, United Planters Association of Southern India Tea Scientific Department, pp. 46-9. Ranganathan, V. and Natesan, S. (1985) Potassium nutrition of tea, in Potassium in Agriculture, (ed. R. D. Munson), Agronomy Society of America, pp. 9811022. Ranganathan V. and Natesan, S. (1987) Manuring of tea - recommendation for high yielding tea fielqs, in Handbook of Tea Culture, United Planters

Association of South India.

Russell, E. W. (1973) Soil Conditions and Plant Growth, 10th edn, Longman, London.

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Sandanam, S. 5., Krishnapillai, S. and Sabaratnam, J. (1978) Nitrification of ammonium sulphate and urea in an acid yellow podzolic tea soil in Sri Lanka in relation to soil fertility. Plant and Soil, 49, 9-22. Scott, R. M. (1962) Summary of the soil survey observations on the Sambret valley. East African Agriculture and Forestry Journal, 27 (special issue), 22. Shaxson, T. F. and Hall, J. N. (1968) Handbook of Recommended Practices for Conservation of Water and Soil in the Tea Areas of Malawi, Tea Research Foundation (Central Africa), Mulanje, Malawi. Sivasubramaniam, S. and Talibudeen, O. (1971) Effect of aluminium on growth of tea and its uptake of potassium and phosphorus. Journal of the Science of Food and Agriculture, 22, 325-9. Sivasubramaniam, S. and Talibudeen, O. (1972) Potassium exchange in acid soils I. Kinetic. Journal of Soil Sciences, 23(2), 165-76. Sombroek, W. G., Braun, H. M. H. and Van der Pouw, B. J. A. (1982) Exploratory Soil Map and Agro-climatic Zone Map of Kenya 1980, Ministry of Agriculture, Nairobi, Kenya. Tea Research Association Annual Report (TRA) (1979/80) Tocklai Experimental Station. Tea Research Foundation of Kenya (TRFK) (1986) Tea Growers Handbook, 4th edn, Kericho, Kenya. Templer, J. c. and Machega, J. S. E. (1978) Replanting tea land to Guatemala grass. Tea, 18(1), 16-17. Thomas, A. S. (1941) Some lessons from a tour of the tea districts of India. East African Agriculture and Forestry Journal, 7, 24. Tolhurst, J. A. H. (1972) A re-appraisal of leaf analysis as a guide to fertilizer programmes. Tea, 13(1), 17-21. Tolhurst, J. A. H. (1973) Zinc Deficiency in Tea. Pamphlet 21173, Tea Research Institute of East Africa, Kericho, Kenya. Willson, K. C. (1966) Hutsites. Tea, 7(2), 22-6. Willson, K. C. (1967) Forms of nitrogen. Tea, 8(3), 11-20. Willson, K. C. (1969) The mineral nutrition of tea. Potash Review, 27, 49, 1-17. Willson, K. C. (1972) Paraquat, mulch and the mineral nutrition in tea. Outlook on Agriculture, 7(2), 74-8.

CHAPTER 6

Tea crop physiology T. W. Tanton

6.1 INTRODUCTION The first tea planters soon discovered that the tea plant needed very specific environmental conditions if it was to produce an economic crop of manufactured tea. Observation along with trial and error led them to identify the general environmental conditions required for commercial tea production and to develop a set of agronomic practices for the effective management of a plantation. The crop needs an acid soil, a humid tropical environment and will not tolerate drought, the best quality tea being produced at high altitudes that remain free from frost. Soils and climatic variables were known to affect the quality of the manufactured tea, the level of yield and the seasonal cropping characteristics of the bush. Having broadly identified the environmental constraints, estates were established in suitable environments and a production system developed that was economically viable. Their observations and practices became established fact and were passed on from one generation of planters to the next. Although such an approach allowed the tea industry to be very successfully and rapidly developed to meet the ever growing demand for tea, it led to a pool of knowledge being accepted as fact despite there being little or no scientific evidence to support it. Scientific examination of the tea crop has proved many of their early observations to be correct but it has also dispelled several established facts about tea as being little more than myth. For example, because tea grows naturally as an understorey tree of the tropical forests of Indo-China it was considered that it always needed be grown under shade, and a considerable amount of time and money was spent maintaining shade trees. However, it is now known that in many tea growing areas greater yields can be obtained in the absence of shade Tea: Cultivation to consumption Edited by K. C. Willson and M. N. Clifford © 1992 Chapman & Hall, London. ISBN 0 412338505

174

Tea crop physiology

(Tea Research Foundation, 1969/70). Other good examples are the peaks and troughs in crop production that occur throughout the season. The peaks in crop production were once thought to be the result of a flush of shoots being produced with active apical buds while the troughs were thought to be the result of shoots being produced with dormant apical buds, known as banjhi shoots. This cycle of dormant shoot production in cropped tea was thought to be controlled by an endogenous rhythm known as the banjhi cycle, although it is now known to be the result of synchronization of growth of the shoot population (Fordham and Palmer-Jones, 1977; Tanton 1981a). Despite the fact that tea is a major world crop and is an essential part of many countries' economies, national governments have been reluctant to invest in research and it has mainly been left to the trade itself to establish and finance much of the running costs of tea research stations. This investment by the trade in Africa has proved a wise investment as implementation of research findings has enabled the trade to implement management practices that have more than doubled its yield per hectare in the past 30 years. This initial large increase in yield has been fairly easy to achieve by adopting fairly simple agronomic practices, and although there is still ample potential to more than double the existing yield, further increases will be more difficult to obtain. If the tea scientists are to lead the way to these higher yields they need a sound understanding of both the biochemistry and physiology of the tea bush within its environment. In this chapter the present state of our knowledge of the tea crop's physiology is discussed and areas where a deeper understanding is needed are highlighted. 6.2 CROP DEVELOPMENT AND COMPONENTS OF YIELD In most tea growing areas of the world tea crops throughout the year, although the size of the crop varies considerably both on a weekly and seasonal basis, with crop yields often being negligible in the coldest weeks of the year. For instance, in Malawi more than 70% of the annual crop is produced in the wet season, from November to March, in a series of three peaks and troughs, each with a period of about 6 weeks, after which the crop declines dramatically from April until August and rises briefly again in September (Fordham and Palmer-Jones, 1977). These fluctuations make it difficult for planters to maintain a regular work force and keep factories working at their optimum efficiency, and it is thus important that the causes of these fluctuations are fully understood. The crop is characterized by the close planted bushes, pruned to a convenient height for harvesting, which grow to form a closed canopy. The pruning and harvesting causes many branched twigs to develop in

Development and components of yield

175

the top 200-400 mm of the bush, in which most of the mature leaves are in the top 150 mm (leaf area index is about 6). New shoots with two or three expanded leaves and a terminal bud are harvested from the top surface of the bush every 7 to 21 days, after which buds in the axils of the topmost leaves of the remaining butts develop to become the next crop. The weight of shoots harvested in any given time therefore depends upon the number of developing shoots per unit area, their rate of growth, and the average weight of shoots at harvest. Examination of the relative importance of these components of yield can give an insight into the effect that cropping practices have on yield. 6.2.1 Pattern of shoot development

There are two models in the literature which describe shoot growth rate. Bond (1942) and Tanton (1979) analyse shoot growth rate data in terms of an exponential rate of shoot extension up to harvestable size, while Herd and Squire (1976) and Squire (1979) analyse shoot growth as having an exponential phase until shoots grow to 2-3 cm and then a linear phase to a harvestable size of 10--15 cm. If the effects of environment on shoot growth are to be studied it is essential to understand why growth can be described by two different models. Measurements of the growth of several thousand shoots have shown that individual shoots grow exponentially to harvestable size, and if measured further they grow in the typically sigmoidal mode described by Bond (1942) and Tanton (1981a). If there is little variation in the rate of growth between individual shoots of a population, the mean growth rate to harvestable size can also be represented by an exponential curve. However, when there is considerable variation between the individual members of a population, the growth rate of the population as a whole must be described as having an exponential and linear phase of growth. The explanation of why this occurs is shown graphically in Fig. 6.1. The mean growth rate of the population is made up of a series of sigmoidal growth curves. All shoots start by growing exponentially but faster developing shoots enter the exponential decay part of their sigmoidal growth while slower growing shoots are still growing exponentially. The additive effect causes a linear phase in the mean growth rate of the population. It is not possible to predict which method should be used to describe growth rate since it will depend on the amount of variation in the sample. The exponential model (Tanton, 1981a) has an advantage when studying the effect of environment on growth rate of a uniform population since only one term is used to describe the growth of a shoot to harvestable size. When growth rates are variable and data for the growth of a population has to be described in two phases, no physiological significance can be placed on the transition point between the two phases since it is a measure of the variability of growth rates.

176

Tea crop physiology

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